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THE DETERMINAIION OF S—SUBSIITUTED TEIRAZOLES

BY REACTION WITH ACID CHLORIDES

By
Coe Durland.Suydam, Junior

A THESIS

Submitted to the College of Science and.Arts of
Michigan State University of.Agriculture and
Applied Science in partial fulfillment of
the requirements for the degree of

MASTER OF SCIENCE

Department of Chemistry

1960

l
Coe Durland Suydam, Jr.

ABSTRACT

S-Substituted tetrazoles were acylated by p—nitrobenzoyl chloride
followed by the formation of 2-substituted-S—p-nitrophenyl-l,3,h-oxa-
diazoles. The method used involved the :refluxing of a sample contain-
ing a weighed amount of tetrazole and an aliquot of a p-nitrobenzqyl
chloride solution in pyridine, and a blank containing the Same aliquot
of reagent solution. It was found that a four to one molar ratio of
acid chloride to tetrazole should be present in the reaction mixture
and that a reflux time from two to fifteen minutes was necessary for
maximum acylation.

The acylation of S-alkyl and aryl tetrazoles was quantitative
within an a : :.cp error ofiQMCJper cent. However, with the exception
of S-diethylaminotetrazole the S—substituted aminotetrazoles were not
quantitatively acylated. This was due to the rearrangement of the
S—substituted aminotetrazole to a l—substituted-S—aminotetrazole which
consumed no acid chloride.

The presence of l-substituted-S—aminotetrazoles did not constitute
an interference in the determination of tetrazoles, but it was found

that 1-substituted tetrazoles did interfere in the determination.

ACKNOWLEDGMENTS

The author is deeply grateful to Dr. Kenneth G. Stone for his
guidance and his help throughout the entire investigation and prep-
aration of this thesis.

Acknowledgment is also extended to Dr. Robert M. Herbst for sup—

plying the tetrazole samples used in this investigation.

VITA

Name: Coe Durllnd Suydam, Jr.

Born: November 17, 1932 in Pittsburg, Pennsylvania

Academic Career: Mamaroneck High School, Mamaroneck, New York

(19h7-19u9)

The Hill School, Pottstown, PennsylVania
(19h9-1951)

St. Lawrence University, Canton, New York
(1955-1958)

Michigan State University, East Lansing, Michigan
(1958- )

Degrees Held: B. S. in Chemistry, St. Lawrence University
(1958)

TABLE OF CONTENTS

Page

I O IN IRODUCI'I- ON I O O O O O O O O O O O O O O O O O O O O O 1

II. EXPERIMENTAL . . . . . . . . . . . . . . . . . . . . . . h
A. Chemicals . . . . . . . . . . . . . . . . . . . . h
B. Solutions . . . . . . . . . . . . . . . . . . . . 5
C. Apparatus . . . . . . . . . . . . . . . . . . . . 5
D. .Acylation Procedure . . . . . . . . . . . . . . . S
E. Titration Procedure . . . . . . . . . . . . . . . 6
F. Calculation of Results . . . . . . . . . . . . . 7

G. Initial work 0 O O O O O O O O O O O O O O O O O 8
III. DISCUSSION OF RESULTS . . . . . . . . . . . . . . . . . . 1h

A. Determination of S-Alkyl and.Ary1 Substituted
TetraZOJ-es . O O O O O C O O O O C O O O O O O O 1h

B. Investigation of the Possible Acylation of
1-Substituted Tetrazoles and 1,5—Disubstituted
Tetrazoles . . . . . . . . . . . . . . . . . . . 18
C. Determination of S-Substituted.Aminotetrazoles . .20
IV . SWY AN D CONCLIBI CNS 0 O O O O O O O O O O O O O O O O 2 9

Him-ATM “TED O O O O O O O O O O O O O O O O O O O . 3 2

TABLE
I.

II.

III.

IV.

VII.

VIII.

IX.

LIST OF TABLES

Relation Between.Per Cent Reaction and #Meq./Mm. . . .

variation of the Acid Strength of the Acylating
Reagent with Time Standing and Reflux Time . . . . . .

Effect of Molar Ratio of Acid Chloride to Tetrazole on
the Quantitative Nature of the Acylation Reaction . .

Effect of varying the Reflux Time on the Quantitative
Nature of the.Acylation Reaction . . . . . . . . . . .

Purity of S-Alkyl and.Aryl Substituted Tetrazoles . .

Determination of S-Alkyl and Aryl Substituted
Tetrazoles by Acylation with p-Nitrobenzqyl Chloride .

Comparison of.Acidimetric and.Aqylation Determinations
0f S‘Stletituted TetraZOIeS o o o o o o o o o o o o 0
Investigation of the Possible Acylation of l-Sub-

stituted and 1,5-Disubstituted Tetrazoles

Purity of S-Substituted.Aminotetrazoles . . . . . . .

Determination of S—Substituted.Aminotetrazoles by
.Acylation with p-Nitrobenzqyl Chloride . . . . . . . .

Summary of Determinations

Page

11

12

13
15

16

17

19
21

22

30

LIST OF FIGURES

Figure Page

1. Titration Curve of p-Nitrobenzqyl Chloride in a
3:1 HZO-Pyridine Solution . . . . . . . . . . . . . . . lO

2. Titration Curve of Purified Product from the
3Acylation of S—Aminotetrazole in a 3:1 H20-
Pyridine SOlution O O C C C O C I . C O O O O O O O O O 2h

3. Titration Curves of Purified Product from the
Acylation of 5<Aminotetrazole . . . . . . . . . . . . . 25

h. Titration Curves of 2—Benzamido-S-phenyl-l,3,h-
OxadiaZOle . O O O C . O O C O . O O . C O O O O O 0 O 27

THE DETERMINATION OF S-SUBSTITUTED TETRAZOLES

BY REACTION WITH ACID CHLORIDES
I. INTRODUCTION

The synthetic chemistry of tetrazoles has been extensively inves-
tigated since 1885 when the first tetrazole synthesis was reported by
Bladin (l), a Swedish chemist.

Inireview article by Benson (2) tetrazoles are described as a
"five membered, doubly unsaturated ring consisting of one carbon and

four nitrogen atoms." .According to the presently accepted system for

numbering the atoms, the ring is drawn as follows:
1 2
“<3
133

The parent compound, tetrazole, itself, can exist in the two tauto-

meric forms I and II. This is true, also of all S-monosubstituted

H433 HQ.

I II

tetrazoles.

One of the most important chemical properties of tetrazoles is
the acidity of those derivatives possessing a hydrogen in the one
position. The dissociation constant for this hydrogen in a number of
monosubstituted tetrazoles has been reported recently by Mihina (3)

who showed that these dissociation constants are about a power of ten

2
lower than the dissociation constants for the corresponding carboxylic
acids.

During all these investigations there has been no Specific deter-
mination for the tetrazole ring reported in the literature. The one
possible exception to this is a determination of tetrazoles based on
their acidity. However, it should be mentioned that this method would
be of little value when the tetrazole is in the presence of other acids.
For this reason most investigators have relied on a Dumas elemental
nitrogen analysis. The obvious disadvantage to this method is that it
cannot differentiate between a ring nitrogen and a substituent nitrogen.

It was the purpose of this investigation to develop a method for
the determination of S-substituted tetrazoles. The particular method
which is presented is based on an article by Hungen gt. El' (h)
which describes the acylation of S—substituted tetrazoles followed by
the formation of 2,5-disubstituted-l,3,h-oxadiazoles. In this commun-
ication Huisgen reported that a number of S-substituted tetrazoles were
100 per cent acylated on a preparative scale by six common acid chlorides
in a pyridine reaction medium. The over—all reaction proceeds as

follows:

R_<:_-I[ + 333-35; Plridine> R-U-R' +HCl + N2
H 1

Assuming the reaction proceeds quantitatively, there are two

 

possible methods for determining the amount of tetrazole which has

reacted. The first method involves a gasometric measurement of the

3
nitrogen gas evolved. The second method, on which this investigation
is based, depends on the acidimetric determination of the acid chloride

which reacts with the tetrazole.

CHEMISTRY m

II. EXPERIMENTAL

A. Chemicals
The chemicals in this investigation were not repurified unless
otherwise stated. Repurification of the tetrazole samples was not
considered necessary since the purity of the compounds could be deter-
mined by an acidimetric titration using standard base. The tetrazole
samples used in this investigation were supplied by Dr. R. M. Herbst,
Professor of Organic Chemistry at Michigan State University.
Chemicals used were:
3,5-Dinitrobenzqyl chloride, Eastman, C.P.
Benzqyl chloride, Eastman, C.P.
Acetyl chloride, Eastman, C.P.
p—Nitrobenzqyl chloride, Eastman, C.P.
Sodium hydroxide, Merck, C.P.
Primary standard used was:
Potassium acid.phthalate, Bakers analyzed primary standard,
oven—dried for two hours at 105°.
Solvents used.were:
Pyridine, Baker's analyzed and Mallinckrodt analytical
reagent
Ethyl acetate, Eastman, C.P.

Dioxane, Eastman, C;P.

B. Solutions

A 0.2N solution of sodium hydroxide was prepared carbonate-free
by dissolving 18 g. of sodium hydroxide in a liter of water, treating
with barium chloride, filtering off the barium carbonate, and making
the solution up to two liters. The solution was protected from carbon
dioxide by a calcium chloride tube filled with ascarite. The solution
was standardized by titrating weighed portions of potassium acid.phthal-
ate'with this solution to a visual end-point using phenolphthalein
indicator (three drops of a l per cent solution in aqueous ethanol).

An approximately 0.2M solution of p—nitrobenzoyl chloride in
pyridine was prepared by dissolving 37.2 g. of p-nitrobenzqyl chloride
in one liter of pyridine. It was found necessary to heat the solution
gently in order to completely dissolve the solid. The solution was

protected from.water vapor.

C.Mmmaum
.A Beckman model H2 pH meter, equipped with a glass electrode and
a saturated calomel electrode, was used for the pH titrations.
For the measurement of nitrogen gas the particular arrangement
used resembles, with modifications, the apparatus designed and construct-
ed by Nicolas and Mansel (S). The modifications include flue use of one
gas buret instead of two, cylinder carbon dioxide, and a three-neck,

round.bottom flask.

D..Aqylation Procedure
With only two variations the acylation of tetrazole samples was

accomplished by refluxing five previously weighed samples and one blank

for two to fifteen minutes. Each sample contained approximately one
millimole of tetrazole and a 20 ml. aliquot 0.2M solution of p-nitro-
benzoyl chloride in pyridine. The blank contained a 20 ml. aliquot
of the 0.2M solution of p-nitrobenzqyl chloride in pyridine. In the
acylation of the monohydrate samples a 25 ml. aliquot of the 0.2M
solution of p-nitrobenzqyl chloride in pyridine was used in all samples
and blanks. Where sample solutions were more suitable, approximately
ten millimoles of tetrazole were weighed out and dissolved in pyridine.
This solution was transferred to a 100 ml. volumetric flask, and 10 m1.
aliquots were used as samples.

After refluxing for the prescribed length of time, the samples
and blank are treated with about 25 ml. of distilled water and removed
from the hot plate on which they were heated.

When the flasks have cooled to room temperature, the solutions
are transferred to hOO m1. beakers. In the process of transferring,
the snail amount of precipitate which clings to the walls of the flask
is dissolved with a small amount of pyridine and also transferred to the

beakers.

E. Titration Procedure
It was realized early in this investigation that a visual end-
point indication would.be impractical in the acidimetric titration of
the refluxed solutions since these solutions were usually highly
colored. As a result it became necessary to use a pH meter and titrate

to a predetermined apparent pH.

7
The standardization control of the pH meter was adjusted to a pH

of seven with a buffered aqueous solution. During the process of the
titration, the samples and blanks were stirred continuously with a
magnetic stirrer. The blank and all samples were titrated with standard

sodium hydroxide to an apparent pH of 9.5.

F. Calculation of Results
The over-all acylation reaction between p-nitrobenzoyl chloride
and any S-substituted alkyl or aryl tetrazole, as described by Huisgen

e_t El: (1;) is asfollows:

R- -H 1 I
+ PYI‘idine > R- ‘0”02 + HCl + N2
02 '

If one considers only the acidity of the acid chloride in the re-

 

action mixture, there is an over—all loss of one equivalent of acidity
for every mole of tetrazole which reacts. It also follows from this
that the value obtained by subtracting the milliequivalents of acidity
of the sample from the milliequivalents of acidity of the blank is a
measure of the millimoles of tetrazole in the original sample if the
acylation reaction is quantitative. Therefore, the quantitative nature
of the acylation reaction can be expressed by the value, #Meq/Mm, when
it is understood that this represents the over-all decrease in the num-
ber of milliequivalents of acidity per millimole of tetrazole in the

sample. Table I shows the relation between per cent reaction and

#Meq./Mm.

TABLE I 8
RELATION BETWEEN PERCENT REACTION AND #MEQ./1VHVI.

 

 

Percent Reaction #Meq./Mm.
O -l.O
25 —O.5
50 0.0
75 0.5
100 1.0

 

G. Initial Work
1. Determination of Most Effective Solvent
Pyridine was chosen as the solvent for the acylation reaction be-
cause this is the solvent used by HuiSQen E$:Ei.(h)° The possibility
of using another solvent was not investigated in this work since

pyridine proved to be effective.

2. Determination of the Most Effective Acylating Agent

The original work in this investigation was carried out using
3,5-dinitrobenzqyl chloride as the acylating agent. The solubility of
this compound in pyridine is high enough to prepare a 0.36SM solution;
however, the solution must be heated in order to completely dissolve
the solid. Once the solid is dissolved, the solution becomes intensely
colored red within two hours. The intense color of this solution was
considered a disadvantage since it was impossible to read the meniscus
of the solution in the process of pipeting aliquots. While early work
with 3,5-dinitrobenzoyl chloride indicated that it could be effectively
used as an acylating agent, it was discarded because of its color.

The next two compounds to be considered were benzoyl and acetyl

chlorides. While these two compounds did not give colored solutions

9
in pyridine, they formed relatively insoluble white precipitates. In

the case of benzoyl chloride, the white precipitate can be dissolved
by heating the solution strongly. However, both benzoyl and acetyl
chlorides were discarded because of the insoluble precipitates which
these two form in pyridine.

The most effective acylating agent was found to be p-nitrobenzoyl
chloride. This compound is easily soluble in pyridine and can be dis-
solved in that solvent with only gentle heating. On the other hand,
this compound resembles 3,5—dinitrobenzoyl chloride in that it also
eventually forms a colored solution. The color, however, forms more
slowly and is not as intense.

It was found that the increase in color intensity was accompanied
by a decrease in acid strength as measured by an acidimetric titration
with standard base using a pH meter. Figure 1 shows a typical apparent
pH titration curve of p-nitrobenzqyl chloride in a 25 per cent aqueous
pyridine solution. It can be seen that the end-point occurs at an
apparent pH value of 9.5. Table II shows the variation of the acidic
strength of this solution with time standing. As a result of this
variation, it was considered necessary to run a blank containing the
same aliquot of acylating solution as in each sample. Also, Table II
depicts the variation in the acidic strength of the acylating reagent
with the length of time refluxed. Again, for this reason it is neces-
sary to reflux the blank for the same length of time that the samples

are refluxed.

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11
TABLE II

VARIATION OF THE ACID STRENGTH OF THE.ACYLATING REAGENT WITH
TIME STANDIM3.AND.REFLUX TIME

 

 

 

 

Time Meq..Acid Found*
Stggfiing Reflux TIme, Min.
0 2 15 30
0 3-879 3.933 3.933 3.925
1 3.906 3.912 3.912 3.912
2 3.871 3.901 3.900 3.887
3 3.801 3.858 3.855 3.855
A 3.77h 3.839 3-837 ---

 

*20 m1. aliquots were titrated to an apparent pH of 9.5 with 0.269bN
NaOH and the strength of the reagent is reported in terms of milli—
equivalents of acidity per 20 ml. aliquot.

3. Determination of the Most Effective Molar Ratio of Acid Chloride

to Tetrazole in the Reaction Mixture

Table III shows the results of varying the ratio of acid chloride
to tetrazole in the reaction mixture. It shows that a molar ratio of
at least 3:1 is necessary in order to make the acylation reaction pro-
ceed quantitatively. The disadvantage of using a large excess of re-
agent is that there is a change of only one milliequivalent in the
presence of six milliequivalents. The experimental conditions used in
this investigation include the use of a hzl molar ratio in order to
insure quantitative acylation in every case. Furthermore, for mono-
hydrate samples it appears necessary to use a 5:1 molar ratio of acid
chloride to tetrazole in order to assure the presence of a four molar

excess of acid chloride for acylation.

12
TABLE III

EFFECT OF‘MOLAR RATIO OF.ACID CHLORIDE TO TETRAZOLE ON THE
QUANTITATIVE NATURE OF THE ACY'LATION REACTION

 

 

 

 

Molar Mg. * M1. of 0.2M NaOH Mmole
Ratio Tetrazole .Acid chloride M1 ‘N Unreacted
Solution ' Tetrazole
5:0 0 25 35.08 0.3009 0
1:1 358.7 12.50 18.19 0.3009 0.55
231 1h8.3 10.00 11.32 0.3009 0.10
321 205.2 21.00 2h.78 0.3009 0.00
hzl 181.h 2h.00 28.90 0.3009 0.00

 

*S-Phenyltetrazole was refluxed with p-nitrobenzqyl chloride for fif-
teen minutes.

A. Determination of the Most Effective Reflux Time

Table IV shows the results of varying the reflux time and its

effect on the quantitative nature of the acylation reaction. As in-

dicated previously, the value of #Meq./Mm. describes the quantitative

nature of the reaction.

It can be seen from Table IV that a reflux

time between two and fifteen minutes is necessary in order to obtain

quantitative acylation.

13

TABLE IV

EFFECT OF VARYING REFLUX TIME ON THE QUANTITATIVE
NATURE OF THE ACYLATION REACTION

 

 

 

Reflux Mg. * Ml. of 0.2M M1. of NaOH
Time Tetrazole Acid chloride for blank - N NaOH #Meq./Mm.
Min. Solution M1. of Na
for sample
360 116.2 20 2.50 0.2691 0.662
120 116.2 20 3.11 0.2691 0.917
60 116.2 20 3.60 0.2691 0.970
30 116.2 20 3.62 0.2691 0.975
15 116.2 20 3.65 0.2691 0.983
2 116.2 20 3.72 0.2691 1.002

 

*S—Phenyltetrazole was refluxed with p-nitrobenzoyl chloride.

**A blank, containing 20 m1. of reagent solution, was run concurrently
with each sample.

III. DISCUSSION OF‘RESULTS

A. Determination of 5-Alky1 and.Ary1 Substituted Tetrazoles

A number of 5—alkyl and aryl substituted tetrazoles were run in
order to assure that acylation of these compounds was quantitative.
Previous to the determination of these samples, the purity of the
tetrazoles used was checked according to the method described in
Experimental Procedures. Table V gives the purity of these samples
titrated as monoprotic acids.

Furthermore, in order to make certain that the acylation procedure
being used.was following the same reaction reported by Huisgen gt al,(1)
the precipitate obtained in the aqylation of 5-phenyltetrazole with
p-nitrobenzqyl chloride was purified by recrystallization in ethyl
acetate. The product of this particular acylation should be 2-pheny1-
5-p—nitropheny1-l,3,h—oxadiazole. Stolle' and Leverkus (7) have re-
ported that this compound has a melting point of 209°C. The melting
point of the substance obtained.was 207°C. On this basis, it was as-
sumed that the acylation processes involved in this investigation and
those reported by Hungenlgt El (1) are the same.

The determination values for the 5-a1kyl and aryl tetrazoles can
be found in Table VI. Also, Table VII compares the acidimetric deter-
mination. Much of the error involved in the deviation between these
two methods of determination can be accounted for by the relatively
high expected error of at least four parts per thousand for the acyla-
tion determination. This error is due to the necessity of taking four

buret readings, each of which includes an error of approximately one

15
part per thousand. The average error for this determination, based on
the comparisons in Table v11, is $0.010 for the #qu./Mm. value. This

would correspond to a ten part per thousand error for this value

TABLEV

6

PURITY OF 5-ALKYL AND ARYL SUBSTITUTED TETRAZOLES

 

 

 

 

 

 

 

 

Mg . NaOH meg/Mm.
Sample Ml . Normality

5-PhenL1te trazo 1e

152.9 5.211 0.2009 1.007

111.6 11.95 0.2009 1.006
5-Me thyltetrazo 1e

181.5 12.25 0.1758 0.982

171.6 11.65 0. 1758 0. 986
5-Benzy1tetrazo 1e

357.3 12.72 0.1758 1.000

3117.11 12.31 0.1758 1.002
5—I—Phenylpropy1te trazole

107.1 12.21 0.1758 0.997

389.2 11.76 0. 1758 0. 999

5- (3 ' -C)yclohexy1;oropyl) te trazo 1e
$111 9J3 a. 03mm Lam
635.0 10.90 ’ 0.3009 1.003

 

   

TABLE VI

ACYLATION WITH p—NITROBENZOYL CHLORIDE

M1. of 0.2M

 

DETERMINATION OF 5-ALKYL.AND.ARYL SUBSTITUTED TETRAZOLES BY

16

 

 

 

 

 

 

-Nitro- Reflux
Mg. P M1. of NaOH
Sample benzoyl N NaOH Time #Meq./Mm.
Tetrazole Chloride Blank Sample Min.
Solution
5-Pheny1tetrazole
1 151.1 20 38.90 33.65 0.2009 2 0.998
2 111.7 20 38.90 31.11 0.2009 2 0.993
3 123.6 20 38.90 31.71 0.2009 2 0.996
1 151.3 20 36.75 31.53 0.2009 2 0.993
5 151.9 20 36.75 31.91 0.2009 2 0.991
5-Methyltetrazole
1 85.9 20 38.81 33.89 0.2009 2 0.967
2 77.3 20 38.81 31.31 0.2009 2 0.976
3 109.0 20 38.81 32.55 0.2009 2 0.970
1 117.5 20 38.81 32.01 0.2009 2 0.972
5 97.5 20 38.81 33.20 0.2009 2 0.971
5-Benzyltetrazole
1 223.8 20 26.18 21.71 0.3009 2 1.020
2 155.7 20 26.18 23.11 0.3009 2 1.013
3 188.0 20 26.18 22.50 0.3009 2 1.020
1 179.7 20 26.18 23.18 0.3009 2 1.032
5 151.0 20 26.18 22.70 0.3009 2 1.013
5:15Phenylpropyltetrazole
1 86.1 20 39.50 37.26 0.2010 2 0.981
2 119.1 20 39.50 31.18 0.2010 2 1.010
3 181.0 20 39.50 31.61 0.2010 2 1.006
1 180.1 20 39.50 31.65 0.2010 2 1.017
5 201.0 20 39.50 31.00 0.2010 2 1.020
5-13 ' -cyc lohexylprgpyl) tetrazo 1e
1 177.8 20 39.10 31.88 0.2010 2 0.993
2 208.7 20 39.10 31.01 0.2010 2 1.008
3 211.1 20 39.10 33.87 0.2010 2 1.009
1 196.1 20 39.10 31.35 0.2010 2 1.001
5 226.2 20 39.10 33.58 0.2010 2 1.005

 

TABLE VII

COMPARISON 0F.ACIDIMETRIC.AND.ACYLATION DETERMINATION
OF 5-SUBSTITUTED TETRAZOLES

 

 

 

 

 

 

 

 

Average .Aoylation
Purity value Deviations
5-Pheny1tetrazole
10m? 0.999 “0.008
0.993 -0.011
00997 -00010
0.991 —0.013
009914 “00613
Avg. 0.012,
5-Methy1tetrazole
0.983 0.967 -0.015
00977 '00006
0.970 -0.012
0.972 -0.010
0.972 {-0.011
Avg. 0.011
5-Benzy1tetrazole
1.0011 1.020 +0.0198
1.013 +0.0122
1.020 +0.0193
1.032 +0.0319
1.013 +0.0128
Avg. "TETEBT"
SarjPhenylpropyltetrazo1e
0.999 0.981 —0.018
1.010 +0.010
1.006 +0.010
1.017 +0.009
1.020 +0.009
Avg. 0.011
5-(3'—chlohexylprqpyl)tetrazole
1.003 0.993 -0.010_
1.008 +0.001
1.009 +0.001
1.001 +0.000
1.005 +0.000
Avg. 0.002

 

18

B. Investigation of the Possible Acylation of l-Substituted

Tetrazoles and 1,5-Disubstituted Tetrazoles.

According to the reaction reported by Hungen §t_al (1), 1-sub-
stituted tetrazoles and 1,5-disubstituted tetrazoles should not be
acylated by the procedure used in this investigation.

It was found, however, that the 1-p-toly1tetrazole consumed acyl—
ating reagent to the extent that it appeared to be about 75 per cent
acylated. It is not known for certain, though, whether this compound
was acylated or underwent some other reaction. Unfortunately, little
work has been done on the reactions of 1-substituted tetrazoles, and
there is no information in the literature concerning this problem.

On the other hand, the 1,5-disubstituted tetrazoles used in this
investigation did not appear to consume acylating reagent. In the
attempted acylation of 1-pheny1-5-aminotetrazole there was a small
apparent consumption of acylating reagent (see Table VIII). However,
previous to the attempted acylation of both of the 1,5-disubstituted
tetrazoles used, a purity check was performed according to the method
described in Experimental Procedures. While the amount of standard
base consumed in these titrations was so small as to preclude an accur-
ate measure of the acidity of these compounds, the samples required
about 0.02 milliequivalents of standard base per millimole of sample.
It is this 0.02 milliequivalents of inherent acidity which accounts
for the #Meq./Mm. value obtained for 1-pheny1-5-aminotetrazole. There-
fore, it would appear from the evidence obtained that neither the
l-phenyl-S-aminotetrazo1e nor the 1—benzyl-5-aminotetrazole consumes

acylating reagent. Moreover, it is interesting to note that there is

TABLE VIII

19

INVESTIEATION OF THE POSSIBLE ACYLATION 0F 1-SUBSTITUTED
TETRAZOLES AND 1,5-DISUBSTITUTED TETRAZOLES

 

 

 

 

 

 

 

M1. of 0.2M
-Nitro- Reflux
Mg. P M1. of NaOH
Sample Tetrazole gfiIgggde Blank Sample N NaOH iii? #Meq./Mm..
l-Tolyltetrazole
1 152.7 20 10.10 37.92 0.2012 2 0.1630
2 156.8 20 10.10 37.16 0.2012 2 0.5161
3 191.1 20 10.10 36. 90 0.2012 2 0.5128
1 175.2 20 10.10 37.18 0.2012 2 0.5105
5 173.3 20 10.10 37.28 0.2012 2 0.5278
6 162.1 20 26.38 25. 25 0.3009 15 0.3380
7 150.6 20 26.38 25.53 0.3009 15 0.2737
8 161.6 20 26.38 25.58 0.3009 15 0.0881
9 156.7 20 26.38 25 00 0.3009 15 0.1502
10 199.1 20 26.38 21. 83 0.3009 15 0.3770
1— Phemy115eaminotetrazole
1 197.9 20 39.31 39.23 0.2015 2 0.0183
2 192.1 20 39.31 39.23 0.2015 2 0.0188
3 196.9 20 39.31 39.23 0.2015 2 0.0181
1 183.3 20 39.31 39.21 0.2015 2 0.0231
5 178.5 20 39.31 39.20 0.2015 2 0.0258
6 205.1 20 38.50 36.66 0.2052 15 0.0111
7 209.1 20 38.50 37.80 0.2052 15 0.0152
8 217.2 20 38.50 37.50 0.2052 15 0.0163
9 198.2 20 38.50 37.03 0.2052 15 0.0215
l-BenzyleS-aminotetrazole
1 210.7 20 26.12 26.38 0.3009 2 -—
2 229.9 20 26.12 26.11 0.3009 2 --
3 258.6 20 26.12 26.10 0.3009 2 --
1 216.9 20 26.12 26.10 0.3009 2 -—
5 250.1 20 26.12 26.12 0.3009 2 --
6 268.6 20 26.36 26.36 0.3009 15 --
7 250.3 20 26.36 26. 33 0.3009 15 --
8 261.3 20 26.36 26.31 0.3009 15 --
9 252.8 20 26.36 26.35 0.3009 15 --
10 318.1 20 26.36 26.35 0.3009 15 --

 

20

no evidence for rearrangement of either of the 1-substituted-5-amino-
tetrazole compounds, to the corresponding 5—substituted aminotetrazoles
as reported by Garbrecht and Herbst (6). If a rearrangement of this
type had occurred, this would have been reflected in a higher #Meq./Mm.
value since the compounds formed.would have been acylated to some

degree.

C. Determination of 5—Substituted Aminotetrazoles

0f the four types of substituted tetrazoles which have been
studied in this investigation, the aminotetrazoles were the only com-
pounds which did not appear to be quantitatively acylated. Previous to
the acylation of these 5—substituted aminotetrazoles a purity check
was performed according to the method described in Experimental Pro-
cedures.(See Table IX). It can be seen from the values of #Meq./Mm.
in Table X that these compounds appeared to be from 60 per cent to
100 per cent acylated; however, there can be noticed much variation in
these values. There is one notable exception to this trend. The acyl-
ation of 5-diethy1aminotetrazole is quantitative.

The results obtained from the acylation of the monosubstituted
aminotetrazoles can be explained in light of the work done by Gar-
brecht and Herbst (6) in which the rearrangement of 5-benzylamino-
tetrazole to 5-amino-l-benzyltetrazole was studied. It was found that
this rearrangement occurred when the compound was held at its melting
point for a few minutes. In a subsequent study using 1-pheny1-5-amino-
tetrazole, it was found that this rearranged by an equilibrium process

as it was possible to go from one isomer to the other.

21
TABLE IX

PURITY 0F 5-SUBSTITUTED.AMINOTETRAZOLES

 

 

 

 

 

 

Mg. NaOH .
Sample .Ml. Normality #Meq./Mm.

5eAminotetrazole monohydrate ‘

231.1 13.02 0.1758 1.012

217.6 13.90 0.1758 1.013
5aAcetylaminotetrazole

270.1 12.11 0.1758 1.001

271.0 12.21 0.1758 0.996
5-Benzy1aminotetrazole

362.6 11.70 0.1758 0.981

351.7 11.11 0.1758 0.983

5-Diethy1aminotetrazole

 

101.9 9.51 0.3009 0.998
158.5 10.80 0.3009 1.001

 

.Assuming that this rearrangement is taking place in the refluxing
solution of tetrazole and acid chloride, it would be expected that the
l—subsituted-5—aminotetrazole formed would not be acylated. This
could account for the low value for #Meq./Mm. for all of the monosub—
stituted aminotetrazoles.

0n the other hand, a semiquantitative gasometric analysis using
the apparatus described.previously in Experimental Procedures, was
made on 5-aminotetrazole in order to collect any nitrogen gas which
might be liberated as a result of acylation. The volume of nitrogen
gas received indicated that the 5-aminotetrazole was being quantitatively

acylated. Again, assuming that this is true, the low value for #Meq./Mm.

TABLE X
DETERMINATION OF 5-SUBSTITUTED.AMINOTETRAZOLES

 

 

 

 

 

 

 

 

M1. of 0.2M
p-Nitro- M1 of NaOH Reflux
Sample ' benzoyl ' N NaOH Time #Meq./Mm.
Tetrazole Chloride Blank Sample Min.
5<Aminotetrazole
1 110.5 25 31.99 32.77 0.3009 2 0.621
2 123.8 25 31.99 31.07 0.3009 2 0.231
3 103.2 25 31.99 32. 90 0.3009 2 0.629
1 108.1 25 31.99 33. 00 0.3009 2 0.571
5 115.9 25 31.99 33.80 0.3009 2 0.319
5-Acetylaminotetrazole
1 128.9 20 10.08 36.17 0.2012 2 0.716
2 126.3 20 10.08 36.58 0.2012 2 0.709
3 113.2 20 10.08 36.09 0.2012 2 0.712
1 110.9 20 10.08 36.11 0.2012 2 0.720
5 112.1 20 10.08 35.89 0.2012 2 0.751
5-Diethylaminotetrazole
1 176.1 20 10.01 33.80 0.2012 2 1.005
2 158.6 20 10.01 31.13 0.2012 2 1.005
3 160.1 20 10.01 31.28 0.2012 2 1.003
1 111.2 20 10.01 35 01 0.2012 2 1.011
5 111.1 20 10.01 35.05 0.2012 2 1.005
5éPhemylaminotetrazole
1 157.6 20 10.02 38. 63 0.2012 2 0.306
2 171.0 20 10.02 38.71 0.2012 2 0.218
3 115.1 20 10.02 38.78 0.2012 2 0.277
1 169.9 20 10.02 38. 90 0.2012 2 0.211
5 175.6 20 10.02 38.93 0.2012 2 0.201
6 111.9 20 38.81 38.01 0.2015 15 0.236
7 111.9 20 38.81 38.25 0.2015 15 0.173
8 111.9 20 38.81 36 10 0.2015 15 0.218
9 111.9 20 38.81 38.21 0.2015 15 0.177
10 111.9 20 38.81 38.16 0.2015 15 0.191

23
TABLE X (Cont.)

     
 

M1. of 0.2M

 

 

 

 

Mg. P‘Nitr°' M1. of NaOH Ref 1""
Sample Tetrazole 8:18:18e Blank Sample N NaOH ;§iflf #Meq./Mm.
5-Benzylamin0tetrazole
1 181.9 20 27.63 23.66 0.3009 2 1.111
2 219.6 20 27.63 23.60 0.3009 2 0.973
3 205.5 20 27.63 21.26 0.3009 2 0.869
1 211.3 20 27.63 23.90 0.3009 2 0.923
5 213.6 20 27.63 23.91 0.3009 2 0.923
6 281.2 20 27.68 21.80 0.3009 15 1.097
7 205.5 20 27.68 23.63 0.3009 15 1.015
8 195.0 20 27.68 21.20 0.3009 15 0.916
9 173.9 20 27.68 21.50 0.3009 15 0.969
10 215.3 20 27.68 21.18 0.3009 15 0.862

 

obtained for 5—amin0tetrazole must be explained by some process other
than incomplete acylation.

The precipitate formed on aoylating 5—aminotetrazole was purified
by recrystallization from dioxane. Figure 2 shows the acidimetric
titration in 25 per cent aqueous pyridine with standard sodium.hydroxide
using a pH meter. It is apparent that the substance acts as a mono-
protic acid. The equivalent weight of this substance, when calculated
from the data presented in Figure 2 is 267.9 g. This value is be-
tween the equivalent weights for 2-amino-5-p-nitr0phenyl-1,3,1-oxa-
diazole and the p-nitrobenzqylated derivative of this compound, 2-p—
nitrobenzamido-S-p-nitropheny1-1,3,1—oxadiazole. This would indicate
that a mixture of these two compounds is formed when 5-aminotetrazole
is acylated with.p-nitr0benzqyl chloride. That the substance isolated

acts as a monoprotic acid in the acylating medium is shown in Figure 3.

21

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26
Curve 1 is an apparent pH titration of a blank containing a 10 ml. ali-
quot of 0.2M solution of p-nitrobenzqyl chloride in pyridine. Curve 2
represents the same aliquot of acylating reagent and a weighed sample
of the substance isolated from the acylation of 5-aminotetrazole. The
equivalent weight of the substance according to the data shown in this
Figure is 261.7 g.

From a similar study in which pure—2—benzamido-5—phenyl-1,3,1-
oxadiazole was titrated acidimetrically in a 25 per cent aqueous pyri-
dine solution and in the acylation medium, it was found that this acts
as a monoprotic acid in both cases (see Figure 1).

This evidence suggests that the acylation of 5-aminotetrazole is
accompanied by one other reaction besides the oxadiazole formation. It
is postulated that after the quantitative formation of the 2-amino—5~p—
nitrophemyl-l,3,1-oxadiaz01e, this compound is partially benzoylated.
The resulting mixture, composed of the 2-amino— and the 2—p-nitrobenz—
amido-1,3,1-oxadiazoles, is titrated as a monoprotic acid. However,
to explain the low results obtained, in Spite of apparent acylation,
both the benzoylated and the unbenzqylated oxadiazoles must be acidic.
The acidity of the benzoylated oxadiazole has been shown. The acidity
of the 2-amino—1,3,1—oxadiazole can be postulated on the basis of the
conjugated system between the amino group and the p-nitrophemyl group
which would have a tendency to delocalize the electrons around the
amino nitrogen toward the oxadiazole ring. The decrease in the
#Meq./Mm. value must be attributed to the milliequivalents of the un-
benzoylated 2-amino—l,3,1-oxadiazole present in the titration mixture

since the milliequivalents of acidity lost due to consumption of reagent

27

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28
in the benzoylation process are gained by the acidity of the benzoylated

2-amino-l,3,1-oxadiazole.

From the preceeding discussion it is evident that the determination
of 5-aminotetrazole and 5—substituted aminotetrazoles by acylation
procedures is complicated by at least two other processes-—the first
which involves the rearrangement of 5-substituted aminotetrazoles and

the second.which involves the formation of acidic substances.

IV} SUMMARY AND CONCLUSIONS

Table XI summarizes the results obtained from the acylation of
the 5—substituted tetrazoles used in this investigation.

It is evident from this table that the acylation of 5-alky1 and
aryl tetrazoles is, within an c: ‘7 error of 11.0 per cent, quanti-
tative by the procedures used. The acylation method used in this work
involved the refluxing of a sample (containing a weighed amount of
tetrazole and an aliquot of a p—nitrobenzoyl chloride solution in pyri-
dine) and a blank (containing the same aliquot of reagent solution).

It was found that a four to one molar ratio of acid chloride to tetra—
zole should be present in the reaction mixture and that a reflux time
from two to fifteen minutes was necessary for maximum acylation.

Nevertheless, it was discovered that with one exception, 5-substi—
tuted aminotetrazoles were not quantitatively acylated. The one excep-
tion to this trend is the quantitative acylation of 5-diethy1amino-
tetrazole.

A number of studies were conducted in order to explain the results
obtained from the acylation of this type of tetrazole. The volume of
nitrogen gas evolved in the acylation of 5-aminotetrazole indicated
that this particular reaction was quantitative. It was also found
that the oxadiazole formed in the reaction was a mixture of 2-amino-
and 2-p-nitrobenzamido-5—p-nitrophenyl-1,3,1-oxadiazole. The benzoyl-
ated compound acts as a monoprotic acid in the titration medium, but

this does not explain the results obtained for 5-aminotetrazole. The

30
TABLE XI

SUMMARY OF DETERMINATIONS

 

 

.Acidimetric Reflux Acylation
Purity Time Determination
Min. value

 

5-Pheny1tetrazole

1.007
5—Methy1tetrazole

0.9831
5-Benzyltetrazole

1.0011
S-YePhenylpropyltetrazo1e

0.9985
5i(3'-qyg10hexy1propy1)tetrazole

1.003
lap-Tblyltetrazole

 

 

 

1-Phenyl-5-amin0tetrazo1e

l-Benzyl-S—aminotetrazo1e

5—Aminotetrazole
1.013
5-Acetylaminotetrazole
0.9983
5-Diethy1aminotetrazole

0.9992
5-Pheny1aminotetrazole

 

 

5—Benzylaminotetrazole
0.9821

0.995
0.972
1.022
1.002
1.005

0.5210
0.3015

0.0209
0.0168

0.000
0.000

0.1716
0.7217

1.006

0.2191
0.1997

0.967
0.981

 

31
acidity lost in benzoylation would be gained from the acidity of the
benzoylated compound. However, the low results obtained for the 5-
Substituted aminotetrazole can be explained by the rearrangement of
the 5-substituted aminotetrazole to a 1-Substituted-5-aminotetrazole
which has been shown to consume no acid chloride.

Furthermore, in order to determine the possible interference of
the presence of l-substitutedtetrazoles, a sample was run and it was
found to consume acid chloride, but not quantitatively.

From the above discussion, the following conclusions can be
drawn:

1. The method described in this investigation can be used to

determine 5-alkyl and aryl substituted tetrazoles.

2. The method described in this investigation cannot be used to

determine 5-Substituted aminotetrazoles.

3. The presence of l-substituted-S-aminotetrazoles does not

constitute an interference in the determination of tetrazoles.

1. The presence of 1-Substituted tetrazoles does constitute an

interference in the determination of tetrazoles.

LITERATURE CITED

Bladin, J. A., Ber., 18, 1511 (1885); through Benson, F. R., Chem.
Rev., 11, 2 (1917).

Benson, F. R., Chem. Rev., 11, 1-61 (1917).

Mihina, J. S., in "The Reaction of Nitriles with Hydrazoic Acid:
Synthesis of Monosubstituted Tetrazoles". Ph. D. Thesis,
Michigan State University (1950).

Huisgen, R., Sauer, J., and Strunn, H. J., Angew. Chem., 70, 272,
(1958).

Nicolas, L., and Mansel, 1., Chim. ana1., 12, 172 (1960).

Garbrecht, W. L., and Herbst, R. M., J. Org. Chem., 18, 1269—91
(1953).

t
Stolle, R., and Leverkus, K. 0., Ber., 16, 1079 (1913).

 

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