Aliphatic and Aromatic Esters

A very important group of flavour molecules is the esters. Many flavour esters can be prepared from organic acids and alcohols from renewable resources. Im- 

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Borane prepared by adding aluminum chloride to a solution of sodium borohydride in diethylene glycol dimethyl ether (diglyme) reduced aliphatic and aromatic esters to alcohols in quantitative yields in 3 hours at 25° using a 100% excess, or in 1 hour at 75° using a 25% excess of lithium borohydride over 2 mol of the hydride per mol of the ester [738] Procedure 20, p. 209). 

Vasiltsova, T.V. et al.. Thermodynamic properties of mixtures containing ionic liquids. Activity coefficients of aliphatic and aromatic esters and benzylamine in l-methyl-3-ethyl-imidazolium bis(trifluoromethyl-sulfonyl)imide using the transpiration method, ]. Chem. Eng. Data, 51,213, 2006. 

The reaction is irreversible and can be used to synthesize aliphatic and aromatic esters. In addition, there are no complications involving water removal or azeotrope formation. Boron tribromide can be used in place of boron trichloride, but the bromide has a stronger tendency to halogenate the alkyl group of the alcohol (26). Boron trifluoride does not give the ester, but gives either a complex or dehydrated product. 

Effect of Plasticizer Shape. Extended plasticizer molecules such as aliphatic chains with a high degree of flexibility, usually lower Tg or Tc much more than bulky plasticizer molecules, such as those containing ring structures. However, Table XIII shows that the comparison between aliphatic and aromatic ester plasticizers is also determined by the length of the alcohol residues and by separation between the ester groups. 

An interesting version of the transesterification reactions was reported by Movassaghi et al., with the amidation of unactivated esters with amino alcohols (Scheme 9.27) [73]. The amidation was explained by carbene-alcohol interactions. A nucleophilic activation of the hydroxyl group of the aminoalcohol 90 by the catalyst 11 is followed by transesterification to the ester 91 which is in-situ-converted to the amide 92 through a N —> O acyl transfer. Various aliphatic and aromatic esters with different functionalities, as well as chiral aminoalcohols, are suitable for this reaction. 

Plasticizers are typically organic liquids of very low volatility, which are miscible with a polymer, and are added to it to improve processability and, in larger amounts (20-80 parts per hundred of resin), to make it soft and flexible, or even rubbery and/or adhesive. The major portion of the plasticizer market (80%) is aliphatic and aromatic esters, which go to convert rigid PVC into flexible PVC. The remainder goes to improve the processability of cellulosics, and for a variety of specialized uses in other polymers. 

The reaction is carried out by heating the ester with 40% aqueous hydrazine hydrate solution. The yields of hydrazides are usually excellent from aliphatic and aromatic esters. The procedure is well il-... 

Both aliphatic and aromatic esters may be converted to amides by electrochemical reduction of the ester in the presence of an amine in a divided cell as in Eq. (23) [95]. This reaction is not formally a reduction, but the reaction does not occur without passage of current. The mechanism is likely formation of an anion radical with abstracts a proton from ammonia to form amide ion. The amide ion subsequently displaces alkoxide in a chain reaction to form carboxamide. 

Applications. Phosphorus(V) oxychloride is mainly used in the manufacture of aliphatic and aromatic esters of phosphoric acid, which are used as flame retardants and plasticizers in plastics, as hydraulic fluids and as extraction agents. 

Other reductions. Miller et report reduction of benzoic acid and of methyl benzoate to benzyl alcohol and of n-butyl caproate to n-butanol and n-hexanoL Russian investigators" report reduction of aliphatic and aromatic esters to aldehydes, of ortho esters to acetals, of acetals to ethers, and of benzyl ethyl ether to toluene. 

The carbonyl group (C=0) gives infrared absorption bands in 1750-1735 cm . The C—H stretching vibrations produce bands in 1300-1180 cm . Aliphatic and aromatic esters may conveniently be analyzed by GC nsing flame ionization detector. A column snch as 10% SP-1000 or 5% FLAP on Chro-mosorb W-HP is suitable for the purpose. 

Ethyl acetate is produced by the yeast, Saccharomyces cerevisiae, using the acetyl alcohol transferase enzyme. It links the acetate from the acetyl-coA with an ethanol molecule. The esters produced can be affected by esterases enzymes, because they hydrolyze the aliphatic and aromatic esters. These enzymes can hydrolyze lipids to obtain medium chain fatty acids (Moreno. 2009). Production of esters is related to the quantity of amino acids. When the nitrogen from the amino acids is high, fatty acids decrease and acyl transferase is not inhibited (Arrizon. 2001). 

In recent years, aliphatic and aromatic esters of phosphoric acids — phosphites — have been recommended more and more often for the stabilization of poljrvinyl chloride and vinyl chloride copolymers. The patent [288] recommends aryl phosphites with long-chain allgrl substituents in the aromatic nuclei it is indicated that such phosphites are complex formers, and hence can be used as agents suppressing the harmful influence of polyvalent metals. The patent [289] recommends phosphites with different radicals in the ester groups ... 

Aromatic and aliphatic amines and some aliphatic and aromatic esters Aromatic and aliphatic amines and some aliphatic and aromatic esters... 

Aliphatic and aromatic esters show an activation effect in the anionic lactam polymerization through a fast acylation of the lactam anion (already at 150 °C) with the formation of the corresponding N-acyl lactam growth center and of an alkoxy anion as by-product [92], The reaction is followed by neutralization of the alkoxy anion [93] ... 

Thiono Esters and Lactones. Although thiono esters can be conveniently prepared via imidates, the introduction of LR for the thionation of esters represents a great advance in synthetic methodology since ordinary esters are used as educts and P4S10 only reacts with esters if enforced reaction conditions are applied, under which many thiono esters decompose. Facile conversion of aliphatic and aromatic esters (eq 10), a,p-unsaturated esters, and lactones to the corresponding thiono derivatives is effected in high yields (eqs 11 and 12). ... 

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