The Chemistry of Nonaqueous Solvents. Volume III: Inert, Aprotic, and Acidic Solvents

410 Pages·1970·5.77 MB·English

by  J.J. Lagowski (Eds.)

Contributors
D. F. BUROW
MARION MACLEAN DAVIS
F. FEHÉR
RAM CHAND PAUL
ALEXANDER I. POPOV
SARJIT SINGH SANDHU
THE CHEMISTRY OF
NOMÇlIEOrS SOLVENTS
Edited by J. J. LAGOWSKI
DEPARTMENT OF CHEMISTRY
THE UNIVERSITY OF TEXAS AT AUSTIN
AUSTIN, TEXAS
Volume III
INERT, APROTIC, AND ACIDIC SOLVENTS
1970
ACADEMIC PRESS New York and London
COPYRIGHT © 1970, BY ACADEMIC PRESS, INC.
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List of Contributors
Numbers in parentheses indicate the pages on which the authors* contributions begin.
D. F. BUROW,* Department of Chemistry, Michigan State University, East
Lansing, Michigan (137)
MARION MACLEAN DAvis,f Institute for Materials Research, National
Bureau of Standards, Washington, D.C. (1)
F. FEHÉR, Institut für Anorganische Chemie der Universität, Cologne,
West Germany (219)
RAM CHAND PAUL, Department of Chemistry, Panjab University, Chandi-
garh, India (187)
ALEXANDER I. POPOV, Department of Chemistry, Michigan State Univer-
sity, East Lansing, Michigan (241, 339)
SARJIT SINGH SANDHU, Department of Chemistry, Panjab University,
Candigarh, India (187)
♦Present address : Department of Chemistry, The University of Toledo, Toledo, Ohio
fPresent address: 5315 29th Street, N.W., Washington, D.C.
Preface
In keeping with the structure established in previous volumes of this
treatise, Volume III consists primarily of critical surveys of specific solvent
systems. The solvent properties of hydrogen sulfide and carboxylic acids are
covered in three chapters. Solution chemistry of sulfur dioxide and acyl
halides is discussed in two chapters. The remaining chapter on Bronsted
acid-base behavior in inert organic solvents complements the discussion of
principles of nonaqueous solution behavior which appeared in Volume I.
The cooperation of the staff of Academic Press is gratefully acknowledged
as is the effort expended by the authors in meeting the necessary deadlines.
Dr. J. M. Lagowski provided invaluable assistance in technical matters.
Without all these contributions, this volume would be an idea rather than a
reality.
J. J. LAGOWSKI
Austin, Texas
June, 1970
Contents of Previous Volumes
VOLUME I PRINCIPLES AND TECHNIQUES
Lewis Acid-Base Interactions in Polar Non-aqueous Solvents
DEVON W. MEEK
Solvation of Electrolytes and Solution Equilibria
ELTON PRICE
Acidity Function for Amphiprotic Media
ROGER G. BATES
Electode Potentials in Non-aqueous Solvents
H. STREHLOW
Solvent Extraction of Inorganic Species
LEONARD I. KATZIN
Experimental Techniques for Low-Boiling Solvents
JINDRIGH NASSLER
Experimental Techniques in the Study of Fused Salts
R. A. BAILEY and G. J. JANZ
Author Index
Subject Index
xii CONTENTS OF PREVIOUS VOLUMES
VOLUME II ACIDIC AND BASIC SOLVENTS
Liquid Hydrogen Chloride, Hydrogen Bromide, and Hydrogen Iodide
FRANK KLANBERG
Anhydrous Hydrogen Fluoride as a Solvent and a Medium for Chemical Reactions
MARTIN KILPARTIGK and JOHN G. JONES
Sulfuric Acid
W. H. LEE
Nitric Acid
W. H. LEE
Amides
JOE W. VAUGHN
The Physical Properties of Metal Solutions in Non-aqueous Solvents
J. C. THOMPSON
Liquid Ammonia
j. j. LAGOWSKI and G. A. MOCZYGEMBA
Author Index
Subject Index
Br^nsted Acid-Base Behavior in
"Inert" Organic Solvents
MARION MACLEAN DAVIS*
Institute for Materials Research
National Bureau of Standards, Washington, D.C,
I. Introduction . . . . . . . . . .2
II. Acid-Base Concepts . . . . . . .. 3
A. Present-Day Concepts . . . . . .. 3
B. Hantzsch's Views about Acidity . . . . .. 4
C. The Role of the Solvent in Ionic Dissociation of Acids, Bases, and
Salts. The Importance of Hydrogen Bonding . .. 5
III. Properties and Classification of Solvents . . . .. 9
A. Dielectric Constants . . . . . . .. 9
B. Bronsted's Classification . . . . . . . 13
C. Comparative Properties of Some "Inert" Solvents . . . 16
IV. Self-Association of Nitrogen-Containing Bases through Hydrogen
Bonding 23
A. Amines . . . . . . . . .. 24
B. Amidines, Guanidines, and Heterocyclic Bases . . 24
V. Self-Association of Acids through Hydrogen Bonding . .. 26
A. Phenols 26
B. Aliphatic and Aromatic Carboxylic Acids . . . . 31
G. Nitric Acid 38
D. Phosphorus-Containing Acids . . . . .. 39
E. Sulfur-Containing Acids . . . . . .. 40
F. ter*-Butyl Hydroperoxide (ί-BuOOH) 41
VI. Evidence for Hydrogen Bonding in Ion Pairs . . . . 41
A. Conductance 41
* Present address: 5315 29th Street, N.W., Washington, D.C. 20015.
1
2 MARION MACLEAN DAVIS
B. Dielectric Polarization . . . . . .. 46
G. Golligative Properties . . . . . . .. 52
D. Spectral Absorption in the Visible and Ultraviolet . .. 55
E. Spectral Absorption in the Infrared . . . .. 65
F. Nuclear Magnetic Resonance Spectroscopy . .. 72
G. Summary and Further Discussion . . . .. 73
VII. Hydrogen Bonding of Neutral Proton Acceptors to Cations . . 74
A. Homoconjugate Cations . . . . . .. 74
B. Heteroconjugate Cations . . . . . .. 76
VIII. Hydrogen Bonding of Neutral Proton Donors to Anions . . 78
A. Homoconjugate Anions . . . . . .. 78
B. Heteroconjugate Anions . . . . . . . 91
IX. Acidity and Basicity Scales in " Inert" Solvents . . .. 98
A. Log K Scales of Acidity and Basicity . . .. 98
BHA
B. Illustrative Tables of Log K , ΔΗ, and AS 103
BHA
X. Acid-Base Titrations in "Inert" Organic Solvents . . .119
A. Introduction . . . . . . . . .119
B. Other Titrations Using Indicator Dyes . . . . .121
C. Instrumental Titrations 122
D. Concluding Remarks . . . . . . .127
References 127
I. INTRODUCTION
This chapter deals with acid-base behavior in organic solvents that are
commonly called inert (an adjective recognized as applying to them in a
comparative, not an absolute, sense). Most of the important examples are
found among aliphatic and aromatic hydrocarbons and their halogen deriva-
tives. Benzene, carbon tetrachloride, chlorobenzene, cyclohexane, and
n-hexane are well-known representatives. Carbon disulfide is included in
the group. Additional adjectives applied to these solvents are aprotic,1
differentiating, indifferent, nondissociating, and nonionizing. In earlier textbooks
of physical chemistry benzene was sometimes termed an associating solvent.
Solvents of this class have low dielectric constants, often as low as 2 to 2.5
and seldom greater than 10. More will be said about solvents in Section III.
The acids of principal interest are hydrogen (Bronsted) acids of familiar
types, e.g., aliphatic and aromatic carboxylic acids and substituted phenols,
all strong enough to have measurable pK values in water. Some mineral
a
acids will also be discussed. The bases of main interest are likewise compounds
that are measurably ionized in water, e.g., aliphatic and aromatic amines
and derivatives of guanidine and pyridine. There has been very little system-
atic study of the interactions of such acids and bases in inert solvents for
several reasons, for example, the long-prevalent, though erroneous, belief
that ionization is a prerequisite to acid-base interactions. Moreover, at-
tempts to apply quantitative acid-base formulations satisfactory for aqueous
Sect. H.A.] 1. BR0NSTED ACID-BASE BEHAVIOR 3
solutions to solutions in benzene, chloroform, etc. met with failure, and
continued study of acid-base systems in inert solvents was not thought likely
to be fruitful. However, since 1945 investigations by absorption spectropho-
tometry (in the visible, ultraviolet, and infrared) have shed much light on
the situation, disclosing that associations through hydrogen bonding, of
various types and strengths, are major determinants of overall acid-base
behavior. By combining such information with results from other kinds of
measurements, notably, conductance, cryoscopy, dielectric polarization, and
nuclear magnetic resonance spectroscopy, it has become possible to con-
struct a coherent picture.
Our aim has been to provide a concise review and discussion of repre-
sentative results, taken partly from work reported in the literature and partly
from experimental work by the author and associates. This chapter is based
largely on a monograph which deals with the same and related topics, but at
greater length and with more extensive documentation.2
It should be pointed out that our discussion contains references to
results obtained for acid-base systems in dipolar aprotic solvents. Since 1960
the appellation ''dipolar aprotic"3 has been applied increasingly to a group
of solvents which resemble aprotic solvents in being relatively inert and
differentiating in character, but differ in having higher dipole moments and
much higher dielectric constants. This second group includes acetone, acetoni-
trile, dimethylformamide, (di) methyl sulfoxide, and nitrobenzene (which
have dielectric constants in the range 20 to 50). Since there are marked par-
allels in acid-base behavior in aprotic and dipolar aprotic solvents, it is
advantageous to consider experimental results available from investigations
using dipolar aprotic solvents in instances where comparable work with
aprotic solvents has not been performed. Correspondingly, results obtained
using aprotic solvents can supply valuable insight into acid-base behavior
in dipolar aprotic solvents.
II. ACID-BASE CONCEPTS
A. Present-Day Concepts
It is well known that the chemist's concept of an acid has undergone
considerable broadening during the twentieth century, and that the term
"acids" now encompasses not merely "hydrogen acids" (compounds con-
taining easily ionizable and replaceable hydrogen), but also numerous non-
hydrogen-containing species ("Lewis acids"4'5). Chemical phenomena
underlying this broadened concept include (i) the similar effects of the two
groups of acids on the color of indicator dyes, and (2) their similar catalytic
properties.