Selective etherification

An interesting example of etherification of close boiling cis and trans 2-tert-butyl-cyclohexanol with .v amylene may be cited. At 353 K, and Indian 130 as cataly.st at 10 % loading, about 94% selectivity for the cis isomer was realized with a feed consisting of about 68.5 % cis and 31.5% trcms isomer (Matkar and Sharma, 1995). 

Clay-supported heteropoly acids such as H3PW12O40 are more active and selective heterogeneous catalysts for the synthesis of MTBE from methanol and tert-butanol, etherification of phenethyl alcohols with alkanols, and alkylation of hydroquinone with MTBE and tert-butanoi (Yadav and Kirthivasan, 1995 Yadav and Bokade, 1996 Yadav and Doshi, 2000), and synthesis of bisphenol-A (Yadav and Kirthivasan, 1997). 

Scheme 5.4, a). Selective etherification of two alcohols based on their difference in hydrophobicity can also be accomplished. When equal amounts of dodecanol and propanol were etherified with benzhydrol in the presence of DBSA in water, benzhydryl dodecyl ether was selectively obtained (Scheme 5.4, b). Thioetherification between a thiol and an alcohol can also be achieved (Scheme 5.4, c). 

The first reactor is a selective hydrogenation reactor, which product is split into LCN and HCN. The LCN cut is substantially S-free and could be directed to etherification... 

In selective etherification, it is important to distinguish between reversible and irreversible reactions. The former class comprises etherifications with dimethyl sulfate, halogen compounds, oxirane (ethylene oxide), and diazoalkanes, whereas the latter class involves addition reactions of the Michael type of hydroxyl groups to activated alkenes. In this Section, irreversible and reversible reactions are described separately, and a further distinction is made in the former group by placing the rather specialized, diazoalkane-based alkylations in a separate subsection. 

Most of the selective-etherification studies on polysaccharides have been made with cellulose, and nearly all of them have involved quantitative separation of the D-glucose derivatives formed on hydrolysis of the partially substituted celluloses. In view of their stability, ethers of polysaccharides are particularly suited to this approach. 

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