The System Pyridine-Hydrogen Chloride As an Acid Medium by Hyman Mitchner a Thesis.Submitted in Partial Fulfilment of the Requir
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THE SYSTEM PYRIDINE-HYDROGEN CHLORIDE AS AN ACID MEDIUM BY HYMAN MITCHNER A THESIS.SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in the Department of CHEMISTRY We accept this thesis as conforming to the standard required from candidates for the degree of MASTER OF SCIENCE Members of the Department of Chemistry THE UNIVERSITY OF BRITISH COLUMBIA APRIL, 1953 ABSTRACT Pyridine salts were investigated as acids in the pyridine system. The mono and the dihydrochloride salts were found to be the best dissolving reagents for the a metals and the sulphides used. Pyridine hydrochloride was most effective in the molten state, whereas pyridine dihydrochloride was found to be quite reactive at room temperature when dissolved in a chloroform solution. Side reactions were investigated and were found to occur only with Mg, Al, and Zn with molten pyridinium chloride. The complex salts, (C5HeN.H)8[MnClB3c5HBN and (C5HBN.H)HgCl4 were isolated and investigated. 1 I AKNOWLEDG-EMENT Sincere appreciation is expressed to Dr. K. Starke for his'encouragement and help in making this work possible. TABLE OF CONTENTS PAGE INTRODUCTION 1. Water as an unique solvent 1 2. Historical approach to reactions in nonaqueous systems a. Confusion and misconcepts in the acid- has e theory.............................. 1 b. Bronsted theory of acids and bases.. «,...© 4- 3. Disadvantages of water as a solvent........... 5 4. Alms of investigation ...... 5 EXPERIMENTAL 1. Purity of reagents 7 2. Preparation of pyridinium salts a. Pyridinium nitrate 7 b. Pyridinium trlchloroacetate 7 Co Pyridinium thiocyanate 8 d. Pyridinium oxalate 8 e. Pyridinium fluoride....................... 9 f. Pyridinium chloride 9 g. Pyridine dihydrochloride................. 11 h0 Other salts of pyridine......... 11 3. Methods of using C5HBN.HC1 and CBHBN.2HC1 a. Molten C5H5N.HC1 and molten CBH6N.2HC1... 12 -11 b. Room temperature systems 1. C.6HBN.HCl in pyridine,,.... ...... 14 lie Saturated chloroform solutions of CBHBN.HC1 and CBHBN.2HC1............ 15 c. The reaction of metals in molten CeHeN.HCl and the reaction of metals with a satur• ated chloroform solution of C6HBN.2HC1 at room temperature..... 16 Solubility of C5HBN.HC1 and CBHBN.2HC1 in. - - chloroform at 23°C 17 Absorbency - wavelength, investigation of the. , chloroform solutions of GBHBN0HC1 and CBH5N.2HC1 17 Side reactions a. Materials i. Preparation of 4-pyridyl-pyridinium dichloride 20 ii. Purification of synthetic quinoline. 20 iii. Preparation of quinoline hydrochlo• ride 21 b. Product of side reactions 1. Isolation............... 22 ii. Examination for bipyridyls. 23 ill. Decomposition product of 4-pyridyl- pyridinium dichloride in NaOH.......... 24 -iii* iv. Further reactions of Zn + C5HBN.HC1 reaction product..................•« 24 c. Reaction of quinoline hydrochloride with metals • . ,. i. Side reaction product ofquinoline, 'hydrochloride plus zinc 25 ii. Reaction of quinoline hydrochloride product with acetic. anhydride 25 7. Reactions with possible analytical application a. Materials - preparation.of. Mn.(OAc )3...... 26 b. Reaction of CBHBN.2HC1 in CHC13 with MnS i. Nature of sample of, MnS 26 ii. Reaction of. manganese, salts,. metal. •. and Mn08 with a saturated chloro• form solution of CBHBN.2HC1..... 27 iii. Heating of a fresh sample of MnS..... 27 iv. Effect of oxidizing agents ..... 27 v. CBHBN.2HC1 in CHC1S on Mh(OAc)8."..... 28 vi. Isolation of the substance confer— ring.the green colour to the G5H5N.2HCI in GHCI3................. 28 vii. Analysis pf the green crystals...... 29 viii. Limit of visible colour...,..,,......,. 29 ix. Colourometric analysis..,,.,....,... 29 x. Variation of colour with time.33 4 -iv- c. Reaction of CBHeN.2HCl in CHC13 with HgS. i. Isolation of the•mercury salt....... 33 ii. Analysis of the mercury salt........ 33 III DISCUSSION lo Pyridine salts as rection media a. Type of reaction most desirable. 37 b. Examination of the pyridine salts pre• pared 37 2. Methods of using CBHBN.HC1 and CBHBN.2HC1 a. Molten state 38 b. Room temperature systems 39 3. The nature of CBHBN.2HC1 in CHC13 Al 4. Side reactions a. Possibility of formation of bipyridyls... 42 b. Ring cleavage............................ 43 c. Limitations due to side reactions 45 5. Reactions with possible analytical application a. Trivalent manganese i. Formulation of the compound (C5HBN.H)sCMnClB3CBH5N............... 46 ii. Explanation of reactions of manganese sstXts© •»••••«*««»••«•««••»• • • •«o«• © • * iii. Determination of trivalent manganese by colourometric analysis of the green complex... 48 -V- b. The mercury-pyridine complex .1. Formulation of the compound (CBHBN»H)gHgCl^••.••••.«•«..««*»•«.. 50 ii. Application of solubility of HgS.... 51 6. Conclusions .. • ... 51 XV BIBLIOGRAPHY. «....-. ...............0........0..... • « 52 TABLES . .......... Table I Reactivity of sulphides in molten C5HeN.HCl and molten CBHBN.2HC1.......*.....*...••..... 13 Table II Reactivity of sulphides in CBHBN.HCi in pyridine. • 14- Table III Reaction of sulphides in saturated chloroform solutions of CBHBN.HC1 and C5HBN.2HC1 15 Table IV The reaction of metals In molten CBHeN.HCl and the reaction of metals with a saturated chloroform solution of C5H6N.2HC1 at room temperature • 16 Table V Reaction of manganese salts, metal and Mn08 with a saturated chloroform solution of CBH BN.2HC1................................... 27 0 -vi- FIGURES Figure I Absorbency-wavelength plot for a saturated chloroform solution of C6HBN.2HC1 and a diluted chloroform solution of CBHBN.HC1... f'lQ i Figure II AbsorbencyTwavelength.plot for a diluted • chloroform solution of C5HBN.2HC1 .. 19 Figure III Spectral-Transmittance curve of green tri• valent manganese complex la a saturated chloroform solution of CBHBN.2HC1.. 31 Figure IV Concentration-Transmittance curve of green trivalent manganese complex in 10 cc. of a saturated chloroform solution of C5H5N.2HCI. Trivalent manganese obtained by reduction Figure V Concentration-Transmittance curve of green trivalent manganese complex in 10 cc. of a saturated chloroform solution of CBH5N.2HC1. Trivalent manganese obtained by oxidation of divalent > manganese, os »».»»•«.»..... •«... 34 Figure VI Variation of colour of green trivalent man• ganese complex with time. .35 -1- I - INTRODUCTION 1. Water as aaunique solvent. Of all our known solvents, the one most used is water. As a solvent, water is considered to be unique. Its physical properties, such as its capacity as a gen- eral solvent for salts and its power of electrolytic dissociation, its low molecular elevation constant, its high boiling point, and its heat of fusion, heat of volatilization, critical, temperature, specific heat, association constant, and dielectric constant with values so much higher than the corresponding values for other substances, all tend to remove it far from other sol• vents and to place it in a class by itself. Furthermore, because of its abundance, it is one of the most studied substances known. ... • 2. .Historical approach to reactions in nonaqueous systems. a. Confusion and misconcepts in the acid-base theory. Following the discovery of the voltaic cell by Volta early in the 19th century, considerable work was done to differentiate between those substances which conduct an electric current in aqueous solutions and those which do not. Electrochemists of the middle 19th century such as Hittorf and Kohlrausch studied the -2- behavlour of the so-called electrolytes such as hydrogen chloride and ammonia in their liquid states. When these latter two substances were found to be nonconductors, it was promptly assumed that they did not break up into ions and that only in water did they possess character• istic chemical and electrochemical properties, and hence only in water was it possible to effect ionic reactions. The criterion for the pure substance to be able to.act as an acid per se was thus related to its ability to conduct electricity. The role of water as an ionizing medium In electro• lytic dissociation intrigued many investigators. Arrhenius (1884) attempted to completely explain electro• lytic dissociation by placing the emphasis on the role 37 of water. Werner , the originator of the complex compound theory, also tried to explain what happened when a nonelectrolyte dissolved in water to give a conducting solution. He introduced the terms "anhydro base" and "aquo base", as well as "anhydro acid" and "aquo acid". "Anhydro bases (such as ammonia) are compounds which combine with the hydrogen ions of water in aqueous solu• tion, and thereby cause a shift in dissociation equili• brium of water until their corresponding characteristic hydroxyl ion concentration has been reached." "Aquo bases (such as potassium hydroxide) are addition compounds of water, which in turn dissociate in aqueous solution to give hydroxy! ions." Anhydro acids (such as HCl) are "compounds which in aqueous solution so combine with hydroxyl ions of water as to cause a shift in dissocia• tion equilibrium of the solvent water until the corres• ponding characteristic hydrogen ion concentration has been reached." It was not long, however, before the limitations of the Arrhenius concept were recognized. Work on non- 36 aqueeus solutions by Walden in Europe and contemporary is activity in the United States by Cady, Franklin , and Kraus made a revision of acid and base theory necessary. It was shown that numerous solvents yielded conducting solutions and that all substances exhibit^solvent prop• erty to a greater or lesser degree.