Aliphatic ester

ALIPHATIC ESTERS Aliphatic esters may be prepared as follows — 

From the acid. The interaction between an acid and an alcohol is a reversible process and proceeds very slowly, for example  

Acetic acid n-Butyl alcohol n-Butyl acetate 

In the conversion of alcohols into alkyl halides, the mechanism is probably  

The reaction therefore involves nucleophilic displacement on carbon passing through the transition state indicated otherwise expressed, the reaction involves nucleophilic displacement in the conjugate acid R—OH2+ in which the displaced group is OH2+- 

The esters of aliphatic dicarboxylic acids, such as adipates, azelates, and sebacates exhibit high plasticizing effectiveness with PVC and 

Tricresyl phosphate Trixylyl phosphate Triphenyl phosphate Triethylphenyl phosphate Diphenylcresyl phosphate Monophenyldicresyl phosphate Dicresylmonoxylenyl phosphate Diphenylmonoxylenyl phosphate Monophenyldixylenyl phosphate Tributyl phosphate Triethyl phosphate Trichloroethyl phosphate Trioctyl phosphate Tris(isopropylphenyl)phosphate 

These types provide an excellent low temperature flexibility 

Likewise, monocaroboxylic acid esters of poly(ol)s show good plasticizing properties. Further, epoxidized fatty acid esters are suitable as plasticizers and as stabilizers for PVC. 

These compounds are capable of forming bonds with hydrogen chloride that is ejected by the decomposition of PVC. 

Two alternative mechanisms are possible for esterification, one is dependent upon an acyl-oxy process (R —CO--OH -f- H OR) and the other an alkyl- 

Acetic acid n-Butyl alcoliol n-ButyI acetate 

Four ions can result from bond cleavage next to 

The ion R+ is prominent in the short-chain esters but diminishes rapidly with increasing chain length and is barely perceptible in methyl hexanoate. The ion R—C=0 gives an easily recognizable peak for esters. In methyl esters it occurs at M — 31. It is the base peak in methyl acetate and is still 4% of the base peak in the 

Now let us consider esters in which the alcohol portion is the predominant portion of the molecule. Esters of fatty alcohols (except methyl esters) eliminate a molecule of acid in the same manner that alcohols eliminate water. A scheme similar to that described earlier for alcohols, involving a single hydrogen transfer to the alcohol oxygen of the ester, can be written. An alternative mechanism involves a hydride transfer to the carbonyl oxygen (McLafferty rearrangement). 

The preceding loss of acetic acid is so facile in steroidal acetates that they frequently show no detectable molecular ion peak. Steroidal systems also seem unusual in that they often display significant molecular ions as alcohols, even when the corresponding acetates do not. 

Esters of long-chain alcohols show a diagnostic peak at m/z 61, 75, or 89,. . . from elimination of the alkyl moiety and transfer of two hydrogen atoms to the fragment containing the oxygen atoms. 

For the general ester, four ions can result from bond cleavage next to C=0. 

Esters of dibasic acids ROOC(CH2) COOR, in general, give recognizable molecular ion peaks. Intense peaks are found at [R00C(CH2) C=0]+ and at [ROOC(CH2) ]+. 

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Examples of the preparation of simple aliphatic esters by Fischer and Speier s method in which an excess of acid is employed are —... 

N-Benzylamides are recommended when the corresponding acid is liquid and/or water-soluble so that it cannot itself serve as a derivative. Phe benzylamides derived from the simple fatty acids or their esters are not altogether satisfactory (see Table below) those derived from most hydroxy-acids and from poly basic acids or their esters are formed in good yield and are easily purified. The esters of aromatic acids yield satisfactory derivatives but the method must compete with the equally simple process of hydrolysis and precipitation of the free acid, an obvious derivative when the acid is a solid. The procedure fails with esters of keto, sul phonic, inorganic and some halogenated aliphatic esters. 

Aromatic esters may be prepared by methods similar to those already described for aliphatic esters (see discussion preceding Section 111,95). These include —... 

The experimental details already given for the detection and characterisation of aliphatic esters (determination of saponification equivalents h3 diolysis Section 111,106) apply equally to aromatic esters. A sfight modification in the procediu-e for isolating the products of hydrolysis is necessary for i)henolic (or phenyl) esters since the alkaline solution will contain hoth the alkali phenate and the alkali salt of the organic acid upon acidification, both the phenol and the acid will be hberated. Two methods may be used for separating the phenol and the acid ... 

Acid Chlorides and Acid Anhydrides of Aromatic Adda, Table IV, 187. Aliphatic Esters, Table III, 106. 

The Claisen condensation of an aliphatic ester and a thiazolic ester gives after acidic hydrolysis a thiazolylketone (56). For example, the Claisen condensation of ethyl 4-methyl-5-thiazolecarboxylate with ethyl acetate followed by acid hydrolysis gives methyl 4-methyl-5-thiazolyl ketone in 16% yield. 

Composition. Shellac is primarily a mixture of aUphatic polyhydroxy acids in the form of lactones and esters. It has an acid number of ca 70, a saponification number of ca 230, a hydroxyl number of ca 260, and an iodine number of ca 15. Its average molecular weight is ca 1000. Shellac is a complex mixture, but some of its constituents have been identified. Aleuritic acid, an optically inactive 9,10,16-trihydroxypalmitic acid, has been isolated by saponification. Related carboxyflc acids such as 16-hydroxy- and 9,10-dihydroxypalmitic acids, also have been identified after saponification. These acids may not be primary products of hydrolysis, but may have been produced by the treatment. Studies show that shellac contains carboxyflc acids with long methylene chains, unsaturated esters, probably an aliphatic aldehyde, a saturated aliphatic ester, a primary alcohol, and isolated or unconjugated double bonds. 

Propionates and higher aliphatic esters generally become less toxic as the si2e of the alkyl carboxylate increases. As an example, the LD q (rat, oral) for ethyl nonanoate [123-29-5] is greater than 43 g/kg, and the LD q (rat, oral) for ethyl heptanoate [106-30-9] is 34.6 g/kg. 

Ethanol [64-17-5] M 46.1, b 78.3 , d 0.79360, d 0.78506, n 1.36139, pK 15.93. Usual impurities of fermentation alcohol are fusel oils (mainly higher alcohols, especially pentanols), aldehydes, esters, ketones and water. With synthetic alcohol, likely impurities are water, aldehydes, aliphatic esters, acetone and diethyl ether. Traces of benzene are present in ethanol that has been dehydrated by azeotropic distillation with benzene. Anhydrous ethanol is very hygroscopic. Water (down to 0.05%) can be detected by formation of a voluminous ppte when aluminium ethoxide in benzene is added to a test portion. Rectified... 

Helmut Orth first reported the use of laetones to accelerate phenolic resole cure in 1957 [161]. A year later, Orth discovered that this effect could be extended to aliphatic esters as well [162], Despite the dramatic nature of the acceleration seen, Orth s observations were not applied in industry for a decade. In 1967, Sumitomo and BASF applied esters to soil grouting and wood uses [133,163, 164]. Neither of these applications were commercially successful, however, and commercial success would not occur until 1980 when Borden introduced ester-cured sand binders for foundry [165]. This technology was highly successful in UK and spread to the US, where it was applied immediately to foundry in 1981 and eventually to wood products in 1990 [119,166-173]. Esters are capable of reducing the gel times of resoles from several weeks to less than 30 s at room temperature. Both gaseous and liquid esters are applicable [119,166]. 

The mechanism of this reaction has been studied by several groups [133,174-177]. The consensus is that interaction of ester with the phenolic resole leads to a quinone methide at relatively low temperature. The quinone methide then reacts rapidly leading to cure. Scheme 11 shows the mechanism that we believe is operative. This mechanism is also supported by the work of Lemon, Murray, and Conner. It is challenged by Pizzi et al. Murray has made the most complete study available in the literature [133]. Ester accelerators include cyclic esters (such as y-butyrolactone and propylene carbonate), aliphatic esters (especially methyl formate and triacetin), aromatic esters (phthalates) and phenolic-resin esters [178]. Carbamates give analogous results but may raise toxicity concerns not usually seen with esters. 

An antipolymerization agent such as hydroquinone may be added to the reaction mixture to inhibit the polymerization of the maleate or fumarate compound under the reaction conditions. This reaction is preferably carried out at a temperature within the range of 20°C to 150°C. This reaction is preferably carried out at atmospheric pressure. Reaction time of 16 to 24 hours have bean specified for this reaction by J.T. Cassaday. The reaction is preferably carried out in a solvent such as the low molecular weight aliphatic monohydric alcohols, ketones, aliphatic esters, aromatic hydrocarbons or trialkyl phosphates. 

The most common types of plasticizer are the phthalic acid esters of Cg, Cio alcohols citric acid esters and epoxy aliphatic esters. 

Many organic liquids, including oils (essential, animal, vegetable or mineral), alcohols, fatty acids, chlorinated hydrocarbons and aliphatic esters, are without action. The absence of any catalytic action of tin on oxidative changes is helpful in this respect. When, however, mineral acidity can arise, as with the chlorinated hydrocarbons containing water, there may be some corrosion, especially at elevated temperature. 

G. Ethyl or Higher Aliphatic Esters of Aromatic Acids... 

Arcus and co-workers94 studied alkaline hydrolyses of neutral and anionic aliphatic esters in the presence of poly (vinylbenzyltriethylammonium hydroxide), 42 (PVBzTEA), as a catalyst. Baumgartner and associate95 also found enhanced alkaline hydrolyses of 43 (aspirin, anionic substrate), in the presence of 42 (PVBzTEA), in alkaline pH regions. 

The three activation parameters, AG, AH, and AS decreased with polyelectrolyte addition. The decrease in AS suggests that the acceleration is due to the enthalpic loss. We recall that the acid hydrolyses of aliphatic esters with polymeric sulfonic acid was accompanied by decreases in AH and AS 97, 98 ... 

Hammet and collaborators140, 141 studied in more detail the hydrolysis of aliphatic esters with a cation-exchange resins as catalyst. They found that replacement of 70% of the hydrogen ions in a crosslinked polystyrenesulfonic add by cetyl-trimethylammonium ions had a specifically favorable effect on the effectiveness of the remaining hydrogen ions for the hydrolysis of ethyl-n-hexanoate. From these findings, the important contributions of the hydrophobic forces, in addition to the electrostatic forces, is clearly demonstrated. 

Sakurada et al.88, 145, 146 hydrolyzed aliphatic esters having various hydrophobicities with cation-exchange resins, Dowex 50 w, and found a close correlation between the accelerating factor and the degree of ester adsorption toward the resins. 

There have been numerous studies on the kinetics of decomposition of A IRK. AIBMe and other dialkyldiazenes.46 Solvent effects on are small by conventional standards but, nonetheless, significant. Data for AIBMe is presented in Table 3.3. The data come from a variety of sources and can be seen to increase in the series where the solvent is aliphatic < ester (including MMA) < aromatic (including styrene) < alcohol. There is a factor of two difference between kA in methanol and k< in ethyl acetate. The value of kA for AIBN is also reported to be higher in aromatic than in hydrocarbon solvents and to increase with the dielectric constant of the medium.31 79 80 Tlic kA of AIBMe and AIBN show no direct correlation with solvent viscosity (see also 3.3.1.1.3), which is consistent with the reaction being irreversible (Le. no cage return). 

The deuterium isotope effect for each hydrogen atom ortho to the diazonio group ( H/ D = 1.22, Swain et al., 1973b) is the largest secondary aromatic hydrogen isotope effect yet observed. It is comparable to those observed for a-deuterium in reactions involving carbocation formation from secondary aliphatic esters. Ob-... 

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