Butyl hydroperoxide and deuteroperoxide. Deuterium isotope effects on hydrogen bonding by Br0nsted acids 40 4.3. Hydrogen-bonded ion pairs 41 4.3.1. Conductance 41 a. Walden's work 42 b. Wynne-Jones' postulate 42 c. Investigations of Kraus, Fuoss, and associates... 43 d. Summary 45 4.3.2. Dielectric constants 46 a. Dielectric polarization of substituted ammonium picrates and halides in benzene 46 b. Dielectric polarization of other acid-base complexes in benzene 47 4.3.3. CoUigative properties 49 a. Cryoscopy 50 Page b. The differential vapor pressure (DVP) method... 51 104 4.5.6. Homoconjugation of other organic and inorganic acids a. Perchloric acid 105 b. Other acids 105 4.5.7. Heteroconjugate anions 105 a. Chemical behavior 105 b. Physical measurements 108 4.6. Concluding discussion of hydrogen bonding 112 4.6.1. Definition of a hydrogen bond. Systems which form hydrogen bonds 112 4.6.2! Some recent concepts of hydrogen bonding 113 5. Acidity and basicity scales in aprotic organic solvents... 114 5.1. Early attempts to determine relative acidities 114 5.2. Log Kbha scales of acidity and basicity 115 5.3. Methods used in determining values of log A^bha 116 5.4. Tables of log ^bha, and AS obtained using aprotic solvents 118 5.4.1. Aromatic and substituted aromatic hydrocarbons 118 a. Benzene 118 b. Anisole and chlorobenzene 126 5.4.3. Carbon tetrachloride 126 5.4.4. Chloroform 128 5.4.5. Miscellaneous aprotic solvents 129 6. Acid-base titrations in completely aprotic solvents 133 6.1. Introduction 133 6.2. Titrations with indicator dyes in completely aprotic solvents 133 6.3. Instrumental procedures for detecting end-points in completely aprotic solvents 133 6.3.1. Conductance titrations 133 iv Contents -Continued Page 6.3.2. Dielectrometric titrations 133 6.3.3. Photometric titrations 134 6.3.4. Thermometric titrations 135 6.3.5. Titrations by the DVP method 135 6.3.6. Cryoscopic titrations 135 6.3.7. Other possible instrumental procedures 135 a. Refractive index 135 b. Density 135 c. Optical rotation 135 6.4. Reference acids and bases for aprotic organic solvents 135 6.4.1. Acids 135 a. Hydrogen chloride 135

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Practical and theoretica l aspects of acid-base reactions in benzene and other organic solvents al'e discussed . The synthesis of the indicators bromphtha lein magenta E and B (the ethyl and n-butyl esters of t etrabromopheno lph thale in ) an d of their t etraalkylammonium salts is descri bed. Qualitative and spectrophotometric data concern in g the color reactions of the indicators with primary, seconda ry, and t ertia ry a li phatic amines , s ubstituted guan idines, a nd other n itrogen bases in benz ene and other types of organic solvents are presen ted. An expla nati on off ered for the color phenom ena is also appli cable to ulfon ephthalcins and other indicators.Examples are given of the qu antitative m eas urement of the relative reactivity of bases with bromphthal ein magenta in benzene. Illust rations a re furnishe d of the app li cation of the ind icato rs to the quantitative estimation of acids and bases, to measu rem ents of the relative s trengt,h s of orga ni c acids, and to the differen tiation o f primary, secondary, and tertiary a liphatic a mines.During t he sp ectrophotometric inves t igations, it was necessar y to des ign new types of a bsorption cells s uitable fo r vo latile solvents a nd for th in laye rs of solu t ion. A desc ription of the e cells is given.

Therlllod vnami c ionizaL ion con sLanLs of 2,3-, 2,5-, 3, ,1-, and 3,5-dini LrophcnoIR in aq ueous solution aL 25° C have beeJl deter min ed by a sp ec trophotome tric me thod. The r e p ectivc valucs fouIld, exprcssed as pK, a rc 4..959, 5.21 0, 5.4.22, and 6.69 2, pK has also been detefm in ed p otenLiometricall y fOf 2,3-and 3,fi-dinitrophenols; t he resp ective valu es obtained a re 4.98 and 6.66 . The experimental pIC \'alues for a ll six dinitroph enols a re lower than Lhe calcu lated valu es based on pK data for pheno l and t.h e mononi trophenols.Spectral absorption curves ar e prese nted for the ionized and uniol1l zed form s of t he four dinit rophellols.

Th e relative acidic strengths ~o f picric acid and t rinitro-m-cresol in benzene have been measured spectrophotometricall y in terms of their reactivi ty with the base, t ribenzylamine. Th e r espective constants found for the combinat ion of tribenzylamine with picric acid and with trinitro-m-cresol in benzene=a t 25° Care 1.58 X 10 3 and 4.48 X 10 2 • The sam e relative order of strengths would be predicted on theoretical grounds. The constant for picric acid is in close agreement wi th previous m ea surements of the dielectric constant of benzene solutions of t ribenzy lammonium picrate. The method used for a ssessm en t of the relat ive strengths of the two 'acids is superior:to m easurem ents of their ionic dissociation in water.

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Th e ther modynami c pK value of picric acid was determin ed spectrophotomet l'i cally in wa ter co n ta ining hy droc hl oric acid to re press the io ni zation . The pI( value 0.33 ( T< "" 0.46) was obtained from data at 45·0 mIL . A ttempts to determin e t he pI( value by poten t iometric tit r ations of picri c acid and by spectr ophoto metri c m easure ments of picr ic acid solution s in t he n car-saturation ran ge did not y ield satisfactor y res ul ts . The n ew pK va lue is comparcd wit h previously published valucs .