Esters from primary alcohols

The ability of hydrolases to hydrolyse esters derived from primary alcohols in the presence of esters derived from secondary alcohols has been recognized (Scheme 3)[11]. 

Reduction of esters by trichlorosilane in tetrahydrofuran in the presence of tert-butyl peroxide and under ultraviolet irradiation gave predominantly ethers from esters of primary alcohols, while esters of tertiary alcohols were cleaved to acids and hydrocarbons. Esters of secondary alcohols gave mixtures of ethers and acids/hydrocarbons in varying ratios. 1-Adamantyl trimethylacetate, for example, afforded 50-100% yields of mixtures containing 2-42% of 1-adamantyl neopentyl ether and 58-98% of adamantane and trimethylacetic acid [1033]. 

Probably the most widely used reagent for partial reduction of esters and lactones at the present time is diisobutylaluminum hydride.44 45 46 47 48 By use of a controlled amount of the reagent at low temperature, partial reduction can be reliably achieved. The selectivity results from the relative stability of the hemiacetal intermediate that is formed. The aldehyde is not liberated until the hydrolytic workup and is therefore not subject to overreduction. At higher temperatures, at which the intermediate undergoes elimination, diisobutylaluminum hydride reduces esters to primary alcohols. 

New reagents, 2-acyloxy-4,6-dimethoxy-133-triazines, have been used as acyiating agents for the synthesis of esters from primary, secondary and tertiary alcohols. Because of mild... 

One of the most important of the properties of tosyl esters is the ease of cleavage of those derived from primary alcohols. In this regard the formation of an iodo compound by reaction with sodium iodide in... 

Aldehydes, RCHO (Sec. 7.9) (Sec. 7.9) (Sec. 8.4) (Sec. 17.7, 19.2) (Sec. 19.2, 21.6) from disubstituted alkenes by ozonolysis from 1,2-diols by cleavage with sodium periodate from terminal alkynes by hydroboration followed by oxidation from primary alcohols by oxidation from esters by reduction with DIB AH [HA1(i-Bu)2]... 

The last two side reactions are fairly easy to control. The reductive dehalogenation appears to be caused by the concomitant oxidation of a primary alcohol (either from the boronic ester or from an alcohol cosolvent). Consequently, it can be minimized simply by utilizing boronic esters from tertiary alcohols (such as pinacol) and by avoiding the use of alcohol cosolvents. Since oxidative homocoupling is facilitated by ambient oxygen, the impact of this side reaction... 

This method is applicable to the preparation of esters from most acids and primary alcohols. Over one hundred of the simpler aliphatic esters of mono- and di-basic acids have been made in this way for a study of their physical properties. The yields of esters from secondary alcohols are only fair. Tertiary alcohols and phenols do not react to an appreciable extent. 

A comparison of the effect of the structure of phosphate esters on uranium extraction from nitrate media shows that the esters from secondary alcohols give higher uranium distribution coefficients (D s) than those from primary alcohols, phenyl esters extract uranium less strongly than alkyl esters, and benzyl esters are intermediate in extractant strength for uranium (24). 

Lithium aminoborohydrides are obtained by the reaction of -BuLi with amine-boranes [FF2, FH5, NT2]. They can be generated in situ as THF solutions or as solids when formed in diethylether or hexane (n-BuLi must then be used in sub-stoichiometric amounts). They are stable under dry air and are slowly decomposed by water [NT2] or methanol so that workup of the reactions mixtures can be carried out with 3M HCl. They reduce alkyl halides (Section 2.1), epoxides (Section 2.3), aldehydes, and ketones (Section 3.2.1) (in the latter case with an interesting stereoselectivity [HFl]), and esters to primary alcohols (Section 3.2.5). a,(3-Unsaturated aldehydes, ketones, and esters are reduced to allyl alcohols (Section 3.2.9) [FF2, FS2]. Depending on the bulkiness of the amines associated with the reagent and to the substrate, tertiary amides give amines or alcohols (Section 3.2.8) [FFl, FF2]. Amines are also formed from imines (Section 3.3.1) [FB1 ] and from azides (Section 5.2) [AFl]. However, carboxylic acids remain untouched. 

Polymer-supported triphenylphosphine ditriflate (37) has been prepared by treatment of polymer bound (polystyrene-2% divinylbenzene copolymer resin) triphenylphosphine oxide (36) with triflic anhydride in dichloromethane, the structure being confirmed by gel-phase 31P NMR [54, 55] (Scheme 7.12). This reagent is effective in various dehydration reactions such as ester (from primary and secondary alcohols) and amide formation in the presence of diisopropylethylamine as base, the polymer-supported triphenylphosphine oxide being recovered after the coupling reaction and reused. Interestingly, with amide formation, the reactive acyloxyphosphonium salt was preformed by addition of the carboxylic acid to 37 prior to addition of the corresponding amine. This order of addition ensured that the amine did not react competitively with 37 to form the unreactive polymer-sup-ported aminophosphonium triflate. 

It should be noted that A-bromo compounds can act as oxidizing agents e.g., A-bromo-acetamide and NBS oxidize secondary alcohols to ketones, and use of this has been made in steroid syntheses.355 Aldehydes, semiacetals, and finally esters are formed from primary alcohols by NBS, and disulfides from thiols (for references see Homer and Winkelmann354). Iodine is liberated from acidified KI solution, a reaction that can be utilized for quantitative determination of NBS and for detection of unchanged NBS in a reaction. 

Acyloxy-4,6-dimethoxy-[l,3,5]-triazines 301, obtained by reaction between carboxylic acids and CDMT 137, have been used as acylating agents for the synthesis of esters from primary, secondary, and tertiary alcohols (Scheme 59). Because of the mild acylation conditions, the method could be applied to esterification of labile alcohols with aromatic and aliphatic acids in good yields <1999S593>. 

Jones s oxidation is a powerful oxidizing medium for the conversion of alcohols to ketones. Unfortunately, this is such a powerful oxidizing medium that unwanted products are possible due to overoxidation. When a primary alcohol such as 1-pentanol (15) reacts with chromium trioxide and aqueous sulfuric acid, it follows the same mechanistic pathway as 9, with formation of chromate ester 16. However, experiments show that the yields of aldehyde from primary alcohols can be very low. 1-Propanol is oxidized to propanal, for example, in only 49% yield, and to obtain the product requires a short reaction time. Very often, a carboxylic acid is formed as a second product or even the major oxidation product rather than the aldehyde. It is known that aldehydes are easily oxidized to carboxyhc acids, even by oxygen in the air. If a sample of butanal were spilled, for example, it is rapidly oxidized to butanoic acid by air. This oxidation is easily detected as the sharp butanal smell is replaced by the pungent butanoic acid smell. Butanoic acid is found in rancid butter and in dirty feet, for example. 

Racemic triacylglycerol (Cl6 0—C4 0—Cl6 0) was used to determine the selectivity of calf pregastric enz5une for esters of primary alcohols sn-1 and sn-3), independent of its selectivity for short-chain fatty acids [15], It was found that the undigested monoacylglycerol recovered from the hydrolysis reaction contained the fom-carbon fatty acid. Kim Ha and Lindsay [10] measured the concentration of the volatile free fatty acids released from ruminants milk fats and foimd that the kid, calf, and lamb pregastric lipases all preferentially catalyzed the hydrolysis of the sn- and sn-3 positions of the glycerides. 

Esters are more easily reduced than carboxylic acids Two alcohols are formed from each ester molecule The acyl group of the ester is cleaved giving a primary alcohol... 

Secondary alcohols (C q—for surfactant iatermediates are produced by hydrolysis of secondary alkyl borate or boroxiae esters formed when paraffin hydrocarbons are air-oxidized ia the presence of boric acid [10043-35-3] (19,20). Union Carbide Corporation operated a plant ia the United States from 1964 until 1977. A plant built by Nippon Shokubai (Japan Catalytic Chemical) ia 1972 ia Kawasaki, Japan was expanded to 30,000 t/yr capacity ia 1980 (20). The process has been operated iadustriaHy ia the USSR siace 1959 (21). Also, predominantiy primary alcohols are produced ia large volumes ia the USSR by reduction of fatty acids, or their methyl esters, from permanganate-catalyzed air oxidation of paraffin hydrocarbons (22). The paraffin oxidation is carried out ia the temperature range 150—180°C at a paraffin conversion generally below 20% to a mixture of trialkyl borate, (RO)2B, and trialkyl boroxiae, (ROBO). Unconverted paraffin is separated from the product mixture by flash distillation. After hydrolysis of residual borate esters, the boric acid is recovered for recycle and the alcohols are purified by washing and distillation (19,20). 

The primary and secondary alcohol functionahties have different reactivities, as exemplified by the slower reaction rate for secondary hydroxyls in the formation of esters from acids and alcohols (8). 1,2-Propylene glycol undergoes most of the typical alcohol reactions, such as reaction with a free acid, acyl hahde, or acid anhydride to form an ester reaction with alkaU metal hydroxide to form metal salts and reaction with aldehydes or ketones to form acetals and ketals (9,10). The most important commercial appHcation of propylene glycol is in the manufacture of polyesters by reaction with a dibasic or polybasic acid. 

Esters of nitro alcohols with primary alcohol groups can be prepared from the nitro alcohol and an organic acid, but nitro alcohols with secondary alcohol groups can be esterified only through the use of an acid chloride or anhydride. The nitrate esters of the nitro alcohols are obtained easily by treatment with nitric acid (qv). The resulting products have explosive properties but are not used commercially. 

Cyclohexanedimethanol (47) starts from dimethyl terephthalate. The aromatic ring is hydrogenated in methanol to dimethyl cyclohexane-l,4-dicarboxylate (hexahydro-DMT) and the ester groups are further reduced under high pressure to the bis primary alcohol, usually as a 68/32 mixture of trans and cis forms. The mixed diol is a sticky low melting soHd, mp 45—50°C. It is of interest that waste PET polymer maybe direcdy hydrogenated in methanol to cyclohexanedimethanol (48). 

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