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(上) 我先讲一些我早期的研究结果。尿素或氨基甲酸酯加热时,即分解成异氰酸酯和胺或异氰酸酯和醇:这是一个吸热反应,我们化了八年时间研究它的机理。并发现主要是R~1_2N~-或R’O~-基脱离而进行解离反应,如将R~1_2N~-基换成Cl或PhO-,则由于这些基团容易成阴离子而脱离,解离反应也非常容易进行;而烷基则不易进行。我们设想如果引入吸电子基团,解离反应可能容易进行,因此曾以α-硝基乙酰胺来进行试验。当时,我们用硝基甲烷的钠盐和异氰酸酯反应,可以得到α-硝基乙酰胺(1)[Michael,A.,Ber.38,22,39’46(1905);Steinkopf,W.and Daege,H.M.,Bet.44,497(1911)],硝基甲烷有一个活泼氢,生成的碳阴离子容易和异氰酸酯发生加成,但得率只有20％。奇怪的是,当我们用硝基乙烷和异氰酸酯反应企图合成α-硝基丙酰胺(2)时,却没有成功。当时,我认为是由于硝基乙烷的钠盐不溶于一般有机溶剂,所以不能反应;为了得到均相的溶液,我试图用三乙胺代替钠来拉掉硝基乙烷的质子。实际上,在硝基乙烷和异氰酸酯的混合物中,加入催化量的三乙胺时,反应非常剧烈,并有CO_2气体放出。
(Above) let me talk about some of my earlier findings. When urea or carbamate is heated, it decomposes into isocyanates and amines or isocyanates and alcohols: It is an endothermic reaction and we have spent eight years researching its mechanism. And found that the main R ~ 1_2N ~ - or R’O ~ - based off the dissociation reaction, such as the R ~ 1_2N ~ - replaced by Cl or PhO-, these groups easily anion as the solution, the solution The reaction is also very easy to carry out; and the alkyl is not easy to carry out. We envisaged that if the introduction of electron-withdrawing groups, the dissociation reaction may be easy, it has been to α-nitro-acetamide to be tested. At that time we were able to obtain α-nitroacetamide (1) by reacting the sodium salt of nitromethane with an isocyanate [Michael, A., Ber. 38, 22, 39’46 (1905); Steinkopf, W. and Daege , HM, Bet. 44, 497 (1911)]. Nitromethane has an active hydrogen and the resulting carbanion readily adds to the isocyanate, yielding only 20%. Curiously, when we attempted to synthesize α-nitropropanamide (2) by reacting nitroethane with an isocyanate, we did not succeed. At the time, I thought it was due to the fact that the sodium salt of nitroethane was not soluble in common organic solvents and therefore could not react; in order to get a homogeneous solution, I tried to pull off the proton of nitroethane with triethylamine instead of sodium. In fact, when a catalytic amount of triethylamine is added to the mixture of nitroethane and isocyanate, the reaction is very vigorous and CO2 gas is released.