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The Synthesis and Thermochemistry of Organoboron and Phosphorus

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The Synthesis and Thermochemistry of Organoboron and Phosphorus The Synthesis and Thermochemistry of Organoboron and Phosphorus Compounds A Thesis submitted by KHAWAJA SABIR HÜ3SAIR in candidature for the degree of Doctor of Philosophy of the University of London Royal Holloway College, Englefleld Green, Surrey. March, 1970. (U.K.;. CLASS N l / V u j AGO. No. I DA ft ACa â u L j j L À ProQuest Number: 10123886 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest. ProQuest 10123886 Published by ProQuest LLC(2016). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code. Microform Edition © ProQuest LLC. ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 "To all those who wished me to reach this stage" AOKNOlVLEDGmmTS The author wishes to express his gratitude to Dr# Arthur Finch for his Invaluable official supervision and encouragement. He Is highly thankful to Dr. P.J. Gardner for his entire supervision, unfailing encouragement and friendly advice. He Is also thankful to all the academic, technical and clerical staff, of the Chemistry Department, Royal Holloway College, for their co-operation and assistance. He wishes to thank the Petroleum Research Fund for a maintenance grant. ABSTRACT The synthesis and standard heats of formation of some substituted arylboroxlnes are reported. Two new aryl- boroxlnes, p-tert-butylphenylboroxlne and p-trlfluoro- methylphenylboroxlne, have been prepared and characterized. The effect of substituting the phenyl ring of triphenyl- boroxlne by, p-fluoro, p-chloro, p-bromo, p-methoxy, p-methyl and o-methyl groups was considered In terms of resonance stabilization of the boroxlnes and the strength of the (aryl) carbon to boron bond. While para-substitution Increases the stability of the arylboroxlnes, ortho substitution decreases It by sterlc effects. Three substituted aryldlchloroboranes were synthesized and thermochemlcally studied. In ortho-tolyldlchloroborane overlap between the ortho-hydrogen and chlorine atoms of the dlchloroboryl group Is proposed to explain the enhanced stability of this compound. Sterlc effects in mesityl- dlchloroborane appear to be dominant and destabilize this compound. Several substituted aryldlhydroxyboranes were prepared. Three of them, para-tolyl, ortho-tolyl and para-carboxy- phenyldlhydroxyboranes were studied thermochemlcally. Solution reaction calorimetry and combustion calorimetry of some phosphorus compounds are reported and standard heats of formation of these compounds were deter­ mined. Several simple aliphatic dlols were combusted In a static bomb calorimeter and their standard heats of formation were derived. CONTENTS PART I o ECTION I page NOMENCLATURE 2 INTRODUCTION 3 SECTION 2 EXPERIMENTAL General techniques 23 (i) Handling and storage 23 (11) Purification of reagents and 23 solvents (111) Elemental Analysis 24 (Iv) Special tests 26 (v) Spectroscopy 27 (VI) Potentlometry 27 (vll) Calorimetry 28 l) Molecular weight Determinations (1) The cryoscoplc method 28 (11) Differential vapour pressure 31 method (C) Determination of Heat of Vapor- 33 Ization SECTION 3 SYNTHESIS AND ANALYSIS (a) Aryldlhydroxyboranes and trlaryl- 38 boroxlnes (b) Aryldlchloroboranes 57 SECTION 4 page RESULTS and DISCUSSION 65 (l) Triarylboroxines 65 (il) Aryldlhalob orane s 91 (111) Aryldlhydroxyboranes 103 (Iv) Conclusion 114 SECTION 5 DETAILED RESULTS 115 PART 2 SECTION 1 INTRODUCTION 134 (a) Phosphorus compounds 134 (b) Simple aliphatic dlols 137 SECTION 2 EXPERIMENTAL (1) General techniques 141 (il) Preparation of pure samples 141 (111) Analytical procedures 143 (Iv) Thermochemistry 145 (a) Phosphorous acid 145 (b) Phenylphosphonous and phenyl 147 phosphonia acids (c) Dlols 149 SECTION 3 page RESULTS and DISCUSSION 154 SECTION 4 SOLUTION REACTION CALORIMETRY 164 SECTION 5 BOMB CALORIMETRY 176 REFERENCES 191 PART I ORGANOBORON COîÆPOUNDS SECTION I NOMENCLATURE The nomenclature of boron compounds has been in a state of flux.^"^ Recently the American Chemical Society Council o has approved a nomenclature for boron compounds and this is as follows I H H - B - H Borane R R - B R Tri-alkyl (or aryl) borane OR RO - B - OR Tri-alkoxy (or phenoxy) borane Cl 1 Cl - B - Cl Boron trichloride Cl R - 3 Alkyl (or aryl) dichloroborane ^ Cl OH R - B Alkyl (or aryl) dihydroxyborane ^ OH 0 / ^ R - B B - R Trl-alkyl (or aryl) boroxlne I 1 0 0 \ / B I R INTRODUCTION There has been rapid development of research in the field of boron chemistry with respect to industrial, technical and medicinal applications* Within the last fifteen years the chemistry of boron compounds has been exhaustively reviewed, e.g. boron-hydrogen, 9.12,13,15.20 boron-oarbon,10'11'16.l8,20,27 ^oron- halogen,^^*^^*^^#^^*^^ boron-phosphorus,^^ boron oxygen^ and boron-nitrogen^^*^^*^^*^^ compounds* pQ^'2’7 Many books dealing with boron compounds are also available and cover most of the recent knowledge about boron and its compounds. The most general procedure for the preparation of organo­ boron compounds is the condensation of a boron compound with an organic halide in the presence of an active metal as the condensing agent.^^ BY, + 6M + 3 R X ------- ^ BR^ + 3MY 4- 3MX k Y a halide, oxide or alkoxide X a halide M a Li, Na, Mg, Zn, Al, Hg or Sn. R a alkyl or aryl group In most oases the intermediate metal-organic halides are isolated and reacted with a suitable substrate resulting in the transference of organic group from metal to boron. The boron substrate may be chosen from a wide range of compounds. The most common are boron halides, trialkoxy- SL borane8 and trialkoxyboroxines. Some of the reactions are shown in the following equationsi Ar2Hg ArBXg + ArHgX ... (46,47) RBXg + RSnX% ... (48-50) -► R3B + 3r< ig x i' ... (54,55) ■HgO BX^4* ¥ (R2 B)gO + W g m + 2SX. ... (53) AIR3 R,3 + AIX3 ... (55-58) ZnPhg SPhBXg + Zn%2 ... (61) f -R MgX - * ■ R B(0R)2 + MgXOR (35-44) Q(OR), + - AlRj -V' RjB + a KOR)^ ... (59) LlPh.NMe, - * ■ pMe2N.Ph.E(0R)2+I10R (63) (R030>3 + R MgX - * > ■ R2B(0R) ... (51) (r 'b o )j or (R2B)20 ... (52) 3Ar^ + LiAr llB(Ar)^ ... (60) The preparation of aryldihydroxyhoranes by the action of a Grignard reagent on trimethoxyborane is conventional. Khotinsky and Melamed^^ used trimethoxyborane and obtained a 50^ yield. Gilman and Vemon^^ claimed 86^ yields by the 59 same procedure. Bean and Johnson reported that tri­ methoxyborane was not suitable for the preparation of aryl- dihydroxy boranes, and claimed an improved yield by using tri-n-butoxyborane at low temperature (-60^0). Washburn et al.^^ reinvestigated the reaction of Garignard reagents with trimethoxyborane and finally developed an incre­ mental method for the preparation of substituted aryldihydroxy- boranes.^^ This method has been used for the preparation of aryldihydroxyboranes in this research. An alternative synthesis of aryldihaloboranes has been the reaction of diarylmercury on boron halides at elevated 6 temperature and pressure. Gilman and Moore^*^ reinvestigated the reaction and reported that the reaction of diarylmercury and boron trichloride occurs very readily at room temperature and atmospheric pressure but it is not instantaneous and needs stirring for thirty minutes* Moreover, 100^ excess of boron trichloride was necessary for the completion of reaction. They prepared aryldihydroxyboranes by the hydrolysis of these aryld ihaloboranes and claimed 70/^ yield of the recrystallized dihydroxyborane. These authors also reported that the substituent in the aryl radical attached to the organomercury compound has a distinct effect upon the reaction. The hydroxy and amino groups, which aid electro- phillo substitution reactions, not only seem to aid the dis­ placement of mercury by boron but also the displacement of boron by a proton.- Thus in these eases the required aryl- dihaloboranes could not be obtained. The carboxy group on the other hand decreases the reactivity of the aryl radical so that the mercury is not displaced by boron even at elevated temperature. Gerrard et al.^^ improved the reaction of arylmercury compounds with boron halides. They prepared a number of substituted arylhaloboranes by the reaction of boron tri­ chloride and tribromide with substituted arylmercury halides in refluxing benzene. In this method 100^ excess of boron- trichloride is not required, the reaction is quantitative. However a slight excess of boron halide is helpful to ensure complete reaction. This method is better than the other available methods^^^^S and shows little isomerization.^^ A brief discussion of isomerization, observed in ortho- tolyldihaloboranes, is relevant in view of the unsuccessful synthesis of 2,6,diraethylphenyldihaloborane. Eggers and 66 Kettle investigated the isomerization of o-tolyldihalo­ boranes and o-xylyldihaloboranes and concluded that this isomerization is due to the migratory aptitude of the o-methyl due to steric crowding. They also proposed that this rearrangement of methyl groups occurs only in the transition state involving the aromatic system and boron halides. Kuetterties^^ investigated this isomerization via the preparation of these compounds by reaction of boron halides and hydrocarbons in the presence of Al* He emphasised the presence of hydrogen halide to form a couple,
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