The Solubility of Hydrogen Chloride in Hydrocarbons at Low Temperatures as a Measure of Basic Properties

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PU B D U B U NIV ERSITY

THIS IS T O CERTIFT T H A T T H E THESIS P R E P A R E D U N D E R M T SUPERVISION

BY_____________ James Denriis B r a d y _______ ___ ______

EimTLED

The Solubility of Hydrogen Chloride in

Hydrocarbons at Low Temperatures as a Measure of Basic Properties._____________________________________

COMPLIES W I T H T H E UNIVERSITY R E G U L A T I O N S O N G R A D U A T I O N T H E S E S

A N D IS A P P R O V E D B Y M E A S FULFILLING THIS P A R T O F T H E R E Q U I R E M E N T S

FOR THE DEGREE OF

_____________Doctor of Philosophy____________________

P R O F E S S O R IN C H A R O E O F T H E S IS

H

September 28

19

ead op

S

chool or

D

epa rtm en t

49

T O T H E LIBRARIAN;-THIS THESIS IS N O T T O B E R E G A R D E D AS CONFIDENTIAL.

P R O F £ 8 S O fi n r O B A B O E

G R A D . SCROOXi F O R M 9 —3 4 9 —I M

THE SOLUBILITY OE HYDROGEN CHLORIDE IN HYDROCARBONS AT LOW TEMPERATURES AS A MEASURE OF BASIC PROPERTIES

A Thesis Submitted to the Faculty

of Purdue University

by James Dennis Brady

In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy

February, 1950

ProQuest Number: 27712218

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ACKNOl/ÏLEDGMSNT

I am most indebted to Professor Herbert C, Brown, who directed this research, for his unlimited patience and daily encouragement.

I also wish to express my appreciation to the

Standard Oil Company of Indiana and to the Purdue Research Foundation for the financial assistance which made this study possible.

TABLE OF CONTENTS

A B S T R A C T .................................................. I N T R O D U C T I O N ..............................................

Page i 1

General Introduction and Review ............. 1 'Solubility of Aromatics and Olefins in Liquid Hydrogen Fluoride ................. 1 Silver Ion Complexes ......................... 2 Dipole Moments of Iodine Solutions 5 Absorption Spectra of Iodine Solutions ...... 7 Solubility of Hydrogen Chloride ........... 8 Hydrogen Bonding ................. 11 Infrared Absorption Studies .................. 12 14 C o n c l u s i o n .......... EXPERIMENTAL P R O C E D U R E .................................. ............. Apparatus and Procedure Procedure for Solubility Determinations at Constant Volume ..................... Constant Temperature Bath (-78.51^C.) ....... Test of Precision of Method .............. Effect of S o l v e n t ............................. Effect of Concentration of Added Aromatic in n-Heptane ......................... Purification of Materials .......

15 15 21 23 25 28 29 31

EXPERIMENTAL R E S U L T S ..................................... 34 Basic Properties of Representative Aromatics..34 Toluene S o l u t i o n .................. 34 n-Heptane Solution ..................... 37 Basic Properties of Isomeric Hydrocarbons ... 40 Basic Properties of Olefinic Compounds ...... 43 Basic Properties of M o n o a l k y l b e n z e n e s ....... 47 Basic Properties of M o n o h a l o b e n z e n e s ........ 52 Basic Properties of Heterocyclics ....... 53 DISCUSSION ...................

56

B I B L I O G R A P H Y .............................................

65

V I T A ......................................................

LISTS OF TABLES AND FIGURES

LIST OF TABLES Table 1,

Page Equilibrium Constants for Complex Formation between Olefins and Silver Ion .. ......

3

Equilibrium Constants for Complex Formation between ........... ^ Aromatic Hydrocarbons and Silver Ion

5

3*

Dipole Moments of Iodine S o l u t i o n s .......

6

4.

Absorption Spectra of Iodine Solutions ......*.......

8

5.

Henry's

Law Constant for Toluene

6.

Henry's

Law Constants for Representative Aromatics .. 29

7.

Henry's

Law Constants for Mesitylene in n-Heptane ... 30

8.

Physical Properties of the C o m p o u n d s ...............

33

9.

Henry's Law Constants for Representative Aromatics in Toluene ..............................

35

Henry's Law Constants for Representative Aromatics in n-Heptane ...................

38

2.

10.

........

26

11.

Henry's

Law Constants for Isomeric Hydrocarbons ..... 41

12.

Henry's

Law Constants for Olefinic Compounds .......

44

13.

Henry's

Law Constants for Diisobutylene

46

14.

Henry's

Law Constant for t e r t - B u t y l b e n z e n e

15.

16.

17. 18.

.............

Solubility of Hydrogen Chloride in the Monoalkyl­ benzenes

48 49

Solubility of Hydrogen Chloride in m-Xylene and Mesitylene

51

Solubility of Hydrogen Chloride in the Monohalo­ benzenes .......

53

Henry's Law Constant for Thiophene ...................

54

LISTS OF TABLES AND FIGURES

LIST OF FIGURES Figure 1.

Page

Apparatus Used for Determining Henry's Law Constants at -78.51^0........

16

2.

Constant Temperature Bath (-78.51^0.)

..............

24

3.

Henry's Law Constant for Toluene ...................

27

4.

Henry's Law Constants for Representative Aromatics in Toluene • ............

36

Henry's Law Constants for Representative Aromatics ......... in n-Heptane

39

6.

Henry's Law Constants for Isomeric A r o m a t i c s

42

7.

Henry's Law Constants for Olefinic Compounds ......

45

8*

Solubility of Hydrogen Chloride in the Monoalkyl­ benzenes and Monohalobenzenes ...................

50

Henry's Law Constant for T h i o p h e n e ........

55

5.

9.

[Contribution from the Department of Chemistry, Purdue University and Purdue Research Foundation] By Herbert C. Brown and James D. Brady

THE SOLUBILITY OF HYDROGEN CHLORIDE IN HYDROCARBONS AT LOW TEMPERATURES AS A MEASURE OF BASIC PROPERTIES^

1.

Contains material from Mr, James D. Brady's Doctoral thesis.

AN ABSTRACT Olefins and aromatic hydrocarbons are known to possess weakly p basic properties . The fact that they dissolve in liquid hydrogen

2.

Hammett, L. P., "Physical Organic Chemistry", McGraw-Hill Book Co., Inc., New York, N.Y., 1940, pp. 292-293.

fluoride

3

4 and coordinate with silver ion , is an indication of basic

3.

Hiatt, von W . , Zeit. anorg. allgem. Chem., 2 3 4 , 189,

4.

Winstein, S. and Lucas, H, J . , This Journal, 60, 1337,

character.

6.

(1937). (1938)

Studies have also been made of dipole moments^ and

Fairbrother, F . , J. Chem. Soc., 1051,

(1948).

11

absorption spectra? of solutions of iodine in aromatic hydrocarbons,

7.

Benesi, H . A . , and Hildebrand, J. H . , This Journal, 71, 2703, (1949).

and these have demonstrated the relative basic properties of a number of aromatic compounds.

The solubility of hydrogen chloride

in a number of organic molecules® has also shown that aromatics

8.

O'Brien, S. J . , ibid., 65, 2709,

(1941).

have electron donor characteristics. The present study was a comparison of basic properties of a number of organic compounds,

carried out by measuring the pressures

of hydrogen chloride over them.

The measurements were performed

in a high vacuum apparatus at -78.51^0.

Henry's law constants were

determined for the solutions and these were used as a measure of relative basicities.

The precision with which the measurements

could be made was demonstrated by the fact that Henry's law constant for toluene (299 mm.), in five runs, was reproducible to whthin one part in three hundred. The basicities for a series of representative aromatic com­ pounds were compared by determining Henry's law constants for solutions of the aromatics in both toluene and n-heptane at -78.51^0. The results are summarized in Table I.

The order of increasing

Ill

Table I Henry's Law Constants for Representative Aromatics at -78,51^0.

Compound

In Toluene

In n-Heptane

Benzotrifluoride

332

4225

Chlorobenzene

318

3997

Benzene

308

3500

Toluene

299

3170

m-Zylene

278

2980

Mesitylene

254

2553

basicity is the order of decreasing Henry's law constants. It was possible to determine small differences in basicity between isomers.

The order of basicities for the xylenes,

tri-

methylbenzenes, and tetramethylbenzenes was found to be xylene < £- xylene < m-xylene < pseudocumene • ArH + HE = ArHg + T .

When the metal salt is added, the metal ion combines with the fluoride ion causing the reaction to the right to be favored. Benzene formed a colorless solution in liquid hydrogen fluoride, toluene and tetralin red-brown, and anthracene, olive green. Hydrogen fluoride alone was not colored by the addition of the above salts. insoluble.

Saturated hydrocarbons were found always to be The above evidence strongly supports the idea that

olefins and aromatic hydrocarbons possess basic properties, whereas saturated hydrocarbons are lacking in such. Silver Ion Complexes. Further evidence for the basicity of olefins is the work of Winstein and Lucas (42), who studied coordination compounds of olefins with silver ion.

The compounds, formed between unsatu­

rated compounds and silver ion, are different from the stable addition compounds produced by usual reagents, such as halogens, in that they are of comparatively low stability. to form the complex is rapid and reversible.

The reaction

The following

general types of olefins were studied, H H H H R-C=CHg, RgCasCHg, R'C=CR, RgCaCR'. ipj^g complexes were studied by the distribution method.

Equilibrium constants were obtained

for the reactions of silver ion with the olefins mentioned. The constants K for the reaction

B + Ag'^ S

ba S

are given in Table 1.

Table 1 Equilibrium Constants for Complex Formation Between Olefins and Silver Ion Substance

K

n-BuCH=CHg

860

Cyclohexene

79.3

EtCH=CHMe

62.7

Me2C=CHg

61.7

Me2C=CHMe

13.3

The equilibrium constant is less, the more deeply the double bond lies in the carbon chain.

Thus, the most stable complex, H it appears, is the one formed from RG-CHg. The expected order,

based on the inductive effects of the groups present, would be the opposite of that found here.

The explanation for the

order observed lies in thesteric interference large groups

involved and tothe large

due to

the

size of the silver ion.

Otherwise, it might be expected, as more alkyl groups accumu-

late around the double bond, the basicity of the olefin, and so the stability of the resulting silver ion complex, should in­ crease.

This work definitely demonstrates the basic character

of olefins, but is not entirely satisfactory since the observed order of ability to coordinate does not correspond to the probable order of increasing basic properties. Recently, studies have been made of complex formation between aromatic hydrocarbons and silver ion (27).

Aqueous

silver nitrate solutions were saturated with benzene, toluene, and the three xylenes and the excess aromatic was extracted with hexane.

The concentration of the aromatic compound in

hexane was determined speotrophotometrically and the amount of free and complexed hydrocarbon was known.

The authors suggest

that two reactions occur, one with one silver ion and one aromatic molecule, the other with two silver ions and one aromatic molecule.

Equilibrium constants were determined for

each reaction and the results indicate that the second reaction is favored as methyl substitution increases. for the two reactions + Ag +

2Ag are given in Table 2.

%1 + + Ar « AgAr

^2 + Ar =

++

AggAr

The constants

Table 2 Equilibrium Constants for Complex Formation Between Aromatic Hydrocarbons and Silver Ion Hydrocarbon

%1

%2

Benzene

.2.95

neglig

Toluene

2.95

0.63

-Xylene

2.89

0.91

m-Xylene

3.03

0.97

p-Xylene

2.63

0.87

0

The results indicate the basic character of aromatics and also that the basicity increases with methyl substitution.

However,

there does not seem to be any correspondence between the relative stabilities of the complexes and the predicted order of basicities. Dipole Moments of Iodine Solutions. Fairbrother (15) has recently studied complexes formed between aromatic hydrocarbons and molecular iodine.

He measured the di­

electric constants and densities of solutions of iodine in cyclohexane, benzene, p-xylene, cyclohexene, dioxane and diisobutylene. From the results, calculations were made of the polarizabilities of the solutions and also the dipole moments. shown in Table 3.

These results are

Table 3 Dipole Moments of Iodine Solutions Solvent

Dipole Moment (D)

Cyclohexane

0.0

Benzene

0.6

p-Xylene

0.9

Cyclohexene

1.1

Diisobutylene

1.5

The formation of the iodine complex is attributed to the electron donor characteristics of the solvent and also to the ease with which an iodine molecule is polarized.

The degree

of polarization of the iodine molecule and the strength of the iodine-solvent bond depends on the basic character of the solvent< Thus, the visible absorption band is most displaced toward the violet (i.e. the solution is browner) in basic solvents and hardly displaced at all in non-basic solvents.

The author

suggests that it is highly improbable that only two distinct types of solutions exist, purple and brown, but rather that a more or less continuous series exists depending on the basicity of the solvent. In this paper, it w a s shown by means of dielectricpolarization measurements that iodine dissolves in a medium of zero or low polarity.

When the solvent possesses bonds or groups

with electron donor character, there results a polarization of the iodine which is accompanied by formation of a red or brown solution.

In cyclohexane which has no donor properties, the

solution is purple and the dipole moment zero.

The results

show that the dipole moments increase in the following order, benzene< p-xylene < cychohexene < dioxane