Hydroalkoxycarbonylation of isobutylene with car bon monoxide and alcohols under conditions of homogeneous catalysis by transition metal complexes is an efficient method for the synthesis of isovaleric acid esters, which find wide practical application.Note that the hydroalkoxycarbonylation reaction of olefins with CO and monohydric alcohols has been widely studied [1]. Of course, the extension of this method to polyols for obtaining polyol esters of car boxylic acids, which are widely used as plasticizers, components of pharmaceuticals and cosmetics, wet ting agents, and emulsifiers, is of practical interest [2]. The esters of polyhydric alcohols are also used in the manufacture of synthetic lubricants [3].There are patent data [2, 4, 5] on the synthesis of polyol esters of carboxylic acids by the hydroalkoxy carbonylation reaction of olefins with carbon monox ide and polyols in the presence of two component cat alyst systems consisting of Co, Ni or Rh compounds (octanoates, stearates, chlorides, or carbonates) and pyridine (or its derivatives).We previously showed the feasibility of the synthe sis of glycolides (glycerides) of isovaleric acid by the isobutylene hydroalkoxycarbonylation reaction at low CO pressures (≤2.0 MPa) in the presence of ethylene glycol (glycerol) and the Pd(Acac) 2 -PPh 3 -TsOH sys tem [6]. The aim of this work was to study the effect of various reaction conditions on the ratio of the prod ucts mono and diglycolides (mono , di , and triglyc erides) of isovaleric acid and to determine the catalytic activity of other systems based on Pd phosphine com plexes.
EXPERIMENTALThe coordination complexes PdCl 2 (PPh 3 ) 2 , Pd(Acac) 2 , and Pd(PPh 3 ) 4 and the ligands PPh 3 , Ph 2 PCH 2 PPh 2 , and Ph 2 PCH 2 CH 2 PPh 2 were obtained according to the procedures described in [7-10]. Commercial reagent grade ethylene glycol and glyc erol were used without special purification. n Tolue nesulfonic acid was recrystallized from 96% ethanol and dried to have the TsOH · H 2 O composition. The experiments were carried out in the solvent free mode.A steel autoclave of 150 mL capacity was charged with 0.035 g (1.1 × 10 -4 mol) of Pd(Acac) 2 , 0.212 g (8.085 × 10 -4 mol) of PPh 3 , 0.263 g (1.386 × 10 -3 mol) of TsOH, and 3.94 g (6.35 × 10 -2 mol) of ethylene gly col or 5.975 g (6.35 × 10 -2 mol) of glycerol. The auto clave was sealed, purged twice with CO to remove air from the system, and then filled with CO to a pressure of 1.0-1.1 MPa. After that, the calculated amount of isobutylene (one or two equivalents relative to ethyl ene glycol or one, two, or three equivalents relative to glycerol) was introduced, and the CO pressure was brought to the desired value. After that, stirring and heating were turned on. The reaction mixture was stirred for varying durations of the process at different temperatures, reactant ratios, and catalyst component ratios. Then, the autoclave was cooled to room tem perature and left to stay overnight. After releasing the pressure to an atmospheric value, the reaction mixture wa...