Long-chain aliphatic alcohols, esterification

Selective oxidations of benzylic and aliphatic alcohols to aldehydes and esters, by O2 in the presence of the ligand Q, o -bis(di-f-butyl phosphino)-o-xylene or Bu"P(l-adamantyl)2 and the additive AgPFg in toluene and in the presence of various alcohols, were achieved using Pd(OAc)2 as the catalyst without the need for additional organic hydrogen acceptors. " In a parallel study, the [PdCl2(MeCN)2]-catalysed esterification of benzylic alcohols with methanol and various long-chain aliphatic alcohols in the... 

How the aliphatic monomers are incorporated into the suberin polymer is not known. Presumably, activated co-hydroxy acids and dicarboxylic acids are ester-ified to the hydroxyl groups as found in cutin biosynthesis. The long chain fatty alcohols might be incorporated into suberin via esterification with phenylpro-panoic acids such as ferulic acid, followed by peroxidase-catalyzed polymerization of the phenolic derivative. This suggestion is based on the finding that ferulic acid esters of very long chain fatty alcohols are frequently found in sub-erin-associated waxes. The recently cloned hydroxycinnamoyl-CoA tyramine N-(hydroxycinnamoyl) transferase [77] may produce a tyramide derivative of the phenolic compound that may then be incorporated into the polymer by a peroxidase. The glycerol triester composed of a fatty acid, caffeic acid and a>-hydroxy acid found in the suberin associated wax [40] may also be incorporated into the polymer by a peroxidase. 

Raghavan and coworkers have reported on the preparation of 4-hydroxybenzoic add esters (parabans) possessing antimicrobial activity by esterification of 4-hydroxybenzoic acid (Scheme 6.153) [299]. Optimum results were obtained using the alcohol (1-butanol) as solvent in the presence of catalytic amounts of zinc(II) chloride or p-toluenesulfonic acid (pTsOH) under atmospheric conditions. After 5 min of microwave irradiation at 120 °C, ca. 40% conversion to the ester was observed. Related studies on the synthesis of long-chain aliphatic esters have been described by Mariani and coworkers [300]. 

The direct esterification of undec-lO-enoic acid with phenylalkanols using DCC and 4-(N,N-dimethylamino)pyridine affords the corresponding esters in quantitative yields. Esterification of the secondary alcohol 655 with long chain aliphatic acids in the presence of DCC and DMAP affords the dioxane esters 656 in yields of 80-93 %. ... 

The aliphatic components of suberin form polyester domains that are attached to the phenolics as indicated above (see Fig. 6.4.7). Activated cu-hydroxy acids and dicarboxylic acids are probably involved in the esterification as shown in cutin biosynthesis (232). It was proposed that the long-chain fatty alcohols found in suberin might be incorporated into the suberin polymer by peroxidase-catalyzed polymerization of phenylpropanoic acid esters of these alcohols (232), such as the ferulic acid esters of C18-C28 alcohols frequently found in suberin-as-sociated waxes (Table 6.4.2). 

Ortho substituents in the aromatic acids retard esterification by the conventional method, but they can be esterified by dissolving in 100% sulfuric acid and pouring the solution into the desired alcohol. This method is applicable to other unreactive systems and was successfully applied to heterocyclic acids, polybasic acids, long-chain aliphatic acids, and several other unreactive substituted aromatic acids. 

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