Notes- Improved Preparation of Triphenylmethyl Perchlorate and Fluoroborate for Use in Hydride Ion Exchange Reactions
Notes- Improved Preparation of Triphenylmethyl Perchlorate and Fluoroborate for Use in Hydride Ion Exchange Reactions
复制标题
注释-用于氢阴离子交换反应的三苯甲基高氯酸盐和氟硼酸盐的改进制备
DOI：
10.1021/jo01078a608
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发表时间：
1960
影响因子：
3.6
通讯作者：
K. Harmon
中科院分区：
文献类型：
--
作者：
H. Dauben;L. Honnen;K. Harmon
In the course of these studies it was found that when trityl halides were used as the hydride ion abstracting reagents, reaction was slow (except in sulfur dioxide solvent) and halide salts formed frequently had undesirable properties, eg, tropenium chloride and bromide were quite hygro-scopic, 5’8 some substituted tropenium ions reacted with halide ions at their substituent groups, 5 and perinaphthenium halides were found to be only transiently stable. 73 For these reasons, use of other trityl salts, particularly those with anions of low nucleophilicity, was investigated. Trityl perchlorate and trityl fluoroborate were found to give rapid hydride ion exchange in a number of different sol-vents and aromatic carbonium ion salt products of unusual stability. 4-7 The consequent need for con-venient routes to these trityl salts led to an examina-tion of the known preparative methods, and has re-sulted in a simplified procedure for the prepara-tion of trityl perchlorate and a convenient new synthesis of trityl fluoroborate. Trityl perchlorate has been prepared by essen-tially three different methods:(i) from trityl chloride and silver perchlorate in nitrobenzene on precipitation by benzene addition9;(ii) from trityl chloride or triphenylcarbinol in nitrobenzene or ether and 71% perchloric acid, followed by re-moval of all water by evaporation in a desic-cator9’10; and (iii) from triphenylcarbinol in acetic anhydride and 71% perchloric acid, the product separating partially from concentrated solution, or by evaporationof dilute solutions in a vacuum desiccator. 10 Method i suffers from the disadvan-tages ofthe need for prior preparationof trityl chloride and the use of explosive silver perchlorate, and method ii requires complete removal of water by slow, and potentially dangerous, evaporation. Method iii, on the other hand, employs a conven-ient starting material and removes the water by reaction with acetic anhydride, but possesses the disadvantage, even when run in concentrated solu-tion, of furnishing conveniently and directly only moderate yields of pure product. However, be-cause of the lower solubility of the salt product in acetic anhydridethan in acetic acid, conduct of the reaction of triphenylcarbinol and 71% perchloric acid in an adequate excess of acetic anhydride leads to the direct separation of yellow crystals of trityl perchlorate in 76-92% yield. Circumvention of the evaporation step not only greatly simplifies the preparation but also avoids formation of a dark-colored product that is not satisfactory for most hydride ion exchange re-actions; decomposition of substituted tropenium
