Alcohol to esters

The mechanisms of the Fischer esterification and the reactions of alcohols with acyl chlorides and acid anhydrides will be discussed m detail m Chapters 19 and 20 after some fundamental principles of carbonyl group reactivity have been developed For the present it is sufficient to point out that most of the reactions that convert alcohols to esters leave the C—O bond of the alcohol intact... 

The conversion of alcohols to esters by O-acylation and of amines to amides by N-acylation are fundamental organic reactions. These reactions are the reverse of the hydrolytic procedures discussed in the preceding sections. Section 3.4 in Part B discusses these reactions from the point of view of synthetic applications and methods. 

The traditional method for transforming carboxylic acids into reactive acylating agents capable of converting alcohols to esters or amines to amides is by formation of the acyl chloride. Molecules devoid of acid-sensitive functional groups can be converted to acyl chlorides with thionyl chloride or phosphorus pentachloride. When milder conditions are necessary, the reaction of the acid or its sodium salt with oxalyl chloride provides the acyl chloride. When a salt is used, the reaction solution remains essentially neutral. 

Complex 77 has also been reported to catalyze the oxidative dimerization of alcohols to esters when the reactions are performed in the presence of base [76]. The presence of base presumably encourages the reversible attack of the alcohol onto the initially formed aldehyde to give a hemiacetal, which is further oxidized to give the ester product. Alcohols 87 and 15 were converted into esters 88 and 89 with good isolated yields (Scheme 20). Alternative iridium catalysts have been used for related oxidative dimerization reactions, and the addition of base is not always a requirement for the reaction to favor ester formation over aldehyde formation [77, 78]. 

Scheldt and co-workers have also illustrated the oxidation of activated alcohols to esters [132], Oxidations of alcohols such as 260 provide the electrophile (acyl donor) for a nucleophilic alcohol 261. Esters 262 are derived from propargylic, allylic, aromatic, and hetero-aromatic substrates (Table 20). The nucleophilic alcohol scope includes MeOH, n-BuOH, f-BuOH, 2,2,2-trichloroethanol, 2-methoxyethanol, and 2-(trimethylsilyl) ethanol. 

Air Oxidation of Alcohols to Esters via Bromine-Nitric Acid Catalysis... 

The Mitsunobu Reaction allows the conversion of primary and secondary alcohols to esters, phenyl ethers, thioethers and various other compounds. The nucleophile employed should be acidic, since one of the reagents (DEAD, diethylazodicarboxylate) must be protonated during the course of the reaction to prevent from side reactions. 

There are various ways wherein esters can be synthesised. An effective method is to react an acid chloride with an alcohol in the presence of pyridine yield. Acid anhydrides also react with alcohols to esters, but are less reactive. Moreover, the reaction is wasteful because half of the acyl content on the acid anhydride is wasted as the leaving group (i.e. the carboxylate ion). If the acid anhydride is cheap and readily available, this method can be used, e.g., acetic anhydride is useful for the synthesis of a range of acetate esters ... 

Maki BE, Chan A, Phillips EM, Scheldt KA (2007) Tandem oxidation of allylic and benzylic alcohols to esters catalyzed by N-heterocyclic carbenes. Org Lett 9 371-374... 

Potassium bromate, KBrOa, and hydrobromic acid are used in the in situ generation of bromine for the oxidation of primary alcohols to esters [742]. 

Ruthenium carbonyl catalyzes the oxidative coupling of alcohols to esters via hydrogen transfer to diphenylacetylene, chalcone, or maleic anhydride... 

I2, alcohol solvent, 15-20h, reflux, 45-94% yield. These conditions also convert acids and alcohols to esters, 0-95% yield. 

The passage of ethanol vapors over such an activated copper catalyst at one atmosphere pressure and about 350° C. at such a rate that only 50 per cent is decomposed results in the conversion of about 11 per cent of the reacted alcohol to ester and the rest to aldehyde. However, when a pressure of 270 atmospheres is employed and the ethanol conducted over the catalyst at 350° C. at a rate equal to four volumes of liquid ethanol per volume of catalyst per hour, about 50 per cent of the alcohol is converted per pass, 5 per cent is decomposed to carbon monoxide and methane and 45 per cent passes through unchanged. Of the alcohol converted about half goes to ethyl acetate, a quarter goes to form M-butyl alcohol, and the remainder forms acetic add and acetaldehyde. These products are separated by a process of distillation and the hydrogen recovered as such. 

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