A few novel methods were developed for the regioselective preparation of p-hydroxybenzoic acid (pHBA) and its amino derivative by means of the Kolbe–Schmitt reaction. Thus, the carboxylation of tetraalkylammonium phenoxide at 125 °C under the CO2 pressure of 5.0 MPa in the presence of K2CO3 gave pHBA in a maximum yield of 56% with the regioselectivity of 97–100%. The carboxylation of potassium phenoxide (PhOK) at 230 °C under the CO2 pressure of 0.5 MPa also gave pHBA regioselectively in a 39% yield, together with unaltered phenol (61%). Under such conditions, the potassium salt of salicylic acid (SA) once formed was transformed into pHBA. Heat treatment of the dipotassium salt of 13C labeled SA indicated that the transformation occurs via two pathways, i.e., the intramolecular rearrangement of the salicylate (66%) and the decarboxylation of the salicylate followed by the recarboxylation of the resulting PhOK (34%). Furthermore, the carboxylation of cesium m-aminophenoxide and 5-amino-1-naphthoxide with CO2 gave regioselectively 4-hydroxyanthranilic and 8-amino-4-hydroxy-1-naphthoic acids, respectively, in good yields. This is a simple one-pot reaction giving these industrially useful acids with good yields.
通过 Kolbe-Schmitt 反应,开发了几种新的方法来区域选择性地制备
对羟基苯甲酸(pHBA)及其
氨基衍
生物。因此,在 125 ℃、
二氧化碳压力为 5.0 兆帕的条件下,在 K2CO3 的存在下对四烷基
铵酚氧化物进行羧化,得到 pHBA,最高收率为 56%,区域选择性为 97-100%。在
二氧化碳压力为 0.5 兆帕的条件下,于 230 摄氏度对苯氧
钾(PhOK)进行羧化反应,也能得到具有区域选择性的 pHBA,收率为 39%,同时还能得到未改变的
苯酚(61%)。在这种条件下,
水杨酸(
SA)的
钾盐一旦形成,就会转化为 pHBA。对 13C 标记的
水杨酸二
钾盐进行的热处理表明,这种转化是通过两种途径进行的,即
水杨酸盐的分子内重排(66%)和
水杨酸盐的脱羧反应,然后是生成的 PhOK 的再羧化反应(34%)。此外,用
CO2 对间
氨基苯酚铯和 5-
氨基-1-
萘氧化物进行羧化,可分别得到具有选择性的
4-羟基
蒽酸和 8-
氨基-
4-羟基-1-
萘酸,而且产率很高。这是一个简单的一锅反应,能以良好的收率得到这些工业上有用的酸。