ACIDITIES OF GLYCINE SCHIFF-BASES AND ALKYLATION OF THEIR CONJUGATE BASES
ACIDITIES OF GLYCINE SCHIFF-BASES AND ALKYLATION OF THEIR CONJUGATE BASES
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DOI：
10.1021/ja00233a031
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发表时间：
1988-12-07
影响因子：
15
通讯作者：
CRIPE, TA
中科院分区：
文献类型：
--
作者：
ODONNELL, MJ;BENNETT, WD;CRIPE, TA
本文报道了六个酮胺Ph2C.bd.NCH(R)CO2Et和五个乙二胺ArCH.DBd.NCH(R)CO2Et在Me2SO中的平衡酸度。将酮胺中的R从H改变为Ph，pKa增加了2.2个单位。Ph取代的这种令人惊讶的酸度下降表明空间效应显著增加，正如观察到的Me和PhCH2取代氢的pKa分别增加3.8和4.2个单位一样。在类似条件下，Ph2C.bd.NCH2CO2Et酮胺的相转移烷基化反应得到90%以上的单烷基化物，而乙二胺4-ClC6H4CH.DBd.NCH2CO2Et在类似条件下得到单烷基和二烷基的混合物。不同的是，单烷基乙二胺的pKa与母体的pKa基本相同，这导致了与母体阴离子的快速平衡和随后的二烷基化。这些母体阴离子和单烷基化阴离子在Me2SO中的烷基化反应速率差异不大，表明决定单烷基化和双烷基化竞争程度的主要因素是母体酸及其单烷基衍生物的相对pKHa，而不是单烷基化和双烷基化反应的相对速率。
Equilibrium acidities in Me2SO are reported for six ketimines of the type Ph2C.dbd.NCH(R)CO2Et and five aldimines, ArCH.dbd.NCH(R)CO2Et. Changing R in the ketimine from H to Ph increased the pKa by 2.2 units. This surprising acidity decrease for Ph substitution points to a substantial increase in steric effect, as do the increases in pKa of 3.8 and 4.2 units observed for the replacement of hydrogen by Me and PhCH2, respectively. Phase-transfer alkylation of the Ph2C.dbd.NCH2CO2Et ketimine gave over 90% of monoalkylate whereas, under similar conditions, the aldimine 4-ClC6H4CH.dbd.NCH2CO2Et gave a mixture of mono- and dialkylate. The difference is that the pKa of the monoalkylated aldimine is essentially the same as that of the parent, which leads to rapid equilibration with the parent anion and consequent dialkylation. The rates of alkylation in Me2SO of these parent and monoalkylated anions did not differ greatly, showing that the relative pKHAs of the parent acid and its monoalkyl derivative, rather than the relative rates of the mono- and dialkylation reactions, is the principal factor that determines the extent of the competition between monoalkylation and dialkylation.