Application of Hydroformylation - Acetalization Tandem Reactions

Although acetals are much less reactive than their aldehyde precursors, under severe conditions conversion is possible. Thus, acetals have been reduced after removal of the hydroformylation catalyst in the presence or absence of water with copper chromite at high temperatures (750 °C) to give the corresponding alcohols [58]. Alternatively, acetals derived from a hydroformylation process have been oxidized in HCOOH to give the corresponding carboxylic acids and formyl esters, respectively [59]. 

The technical Co-catalyzed hydroformylation-acetalization of acrylonitrile with methanol has been claimed by Dow [60]. It was found that the addition of a basic promoter, such as HN(CH2CN)2, enhances the product selectivity with Co2(CO)g as catalyst at 100 at syngas and 100 C. Alternatively, quaternary ammonium salts, such as N-benzyl-MdVdV-trimethylammonium methoxide, have been suggested to increase the rate of the reaction with long-chain olefins [61]. Up to 90% yield of acetal was noted at 100% conversion of the olefin. Sn[Co(CO)4]4 is an efficient catalyst for the hydroformylation-acetalization of 1-hexene [62]. It was proven that the acetalization reaction is mediated by the Lewis-acidic Sn moiety. 

In a similar manner, Packett at Union Carbide realized a one-pot rhodium-catalyzed version of the methodology by using diols (ethylene glycol, 1,4-butane-diol, or 2,3-butanediol) as acetalization reagents and pyridinium tosylate as co-catalyst [12]. As ligands, bidentate diphosphites and diphosphines were utilized. Under these conditions, the main products were the corresponding diacetals (up to 55%), whereas in the absence of diols mainly isomeric pentenals ( 80%) and valeraldehyde ( 10%) were obtained. 

The hydroformylation-acetalization of 1-octene was investigated with Cl2Pt(COD) and tra s-l,2-bis(diphenylphosphinomethyl)cyclobutane as ligand in methanol [41]. A similar active system was generated from [Pt(acac)(COD)]Bp4. 

Both catalytic systems benefited from the presence of SnCl2. 

---