Pear ester

Problems Pear ester (43) is an important industrial flavouring compound with a pear-like taste and smell. Consider all possible Wittig disconnections and choose a reaction which should give the right geometrical isomer. 

In 2004, Ley et al. [45] showed a stereoselective enzymatic synthesis of cis-pellitorine [N-isobutyldeca-(2 ,4Z)-dienamide], a taste-active alkamide naturally occurring in tarragon. The reactants were ethyl ( ,Z)-2,4-decadienoate— the pear ester described before—and isobutyl amine. The reaction is catalysed by lipase type B from Candida antarctica (commercially available), which shows a remarkable selectivity towards the 2 ,4Z ester. The yield was about 80%. 

Polyunsaturated aliphatic alkohols, aldehydes, ketones, and esters occur as fragrance components in fats, oils, fruits and plants 158). As an example the synthesis of ethyl (2 ,4Z)-2,4-decadienoate (232, pear ester ), which is responsible for the aroma of bartlett pears 161) is given. 2,4-Diunsaturated ester 232 may be obtained by a number of highly stereoselective syntheses, a lot of them making use of the Wittig reaction. Ohloff and Pawlak condensed 4,5-epoxy-( )-2-pentenal 228 with the ylide generated from 229 (butyllithium/ether) to the alkadiene epoxide 230 which was oxidized with periodic acid to the 2,4-decadienal 231. 231 is subsequently converted with MnOj/NaCN in ethanol to the pear ester 232162) [75 % (Z)-amount of the C-4 double bond] (Scheme 44). 

A synthesis elaborated by the BASF affords directly pear ester 232 with about 85 % of the isomer with (Z)-geometry of the C-4 double bond. This synthesis involves reaction of phosphorane 93 with fumaric ester aldehyde 233 (sodium amide technique). The latter is formal by ozonolysis of sorbic ester163) (Scheme 45). Principally, the same method was published by a Belgian research group, leading to 70% of (2 ,4Z)-2,4-isomer 164>. 

A synthesis of the pear ester worked out in our laboratory uses the (Z)- and the ( )-stereoselective Wittig olefination for the generation of the two double bonds in the molecule 232165). Reaction of 2-ethoxyvinyl-triphenylphosphonium bromide 234 with one equivalent sodium ethanolate yields 2,2-ethoxyethylene-triphenyl-phosphorane 235166,167). (Z)-Stereoselective olefination of 235 with hexanal 236... 

Synonyms 2,4-Decadienoic acid, ethyl ester, (E,Z)- Ethyl 2,4-decadienoate Ethyl (2E,4Z) decadienoate Ethyl (2E,4Z)-2,4-decadienoate Ethyl 2-trans-4-cis-decadienoate E,Z-Ethyl 2,4-decadienoate Ethyl trans-2-cis-4-decadienoate Ethyl trans-2-cis-4-decadienoate, mixt. of isomers Pear ester Definition One of the principle components of pear Empirical C12H20O2... 

Pea Pro-Tein BK Pea protein hydrolysate. See Hydrolyzed pea protein Pear ester. See Ethyl decadienoate Pearex L See Pectinase Pearl AP. See Corn (Zea mays) starch Pearl / Pearl II, Pearl III. See Bismuth oxychloride... 

Et ester [3025-30-7]. Pear ester. Constit. of odoriferous principle of Bartlett pears. Bpo.05 84-86 . 4-Bromophenacyl ester Mp 72 . 

Current research focuses on new compounds that attract both males and females. One such example is ethyl (2E,4Z)-2,4-decadienoate, known as the pear ester ... 

Aliphatic esters in various combinations play a major part in many flavors, particularly fruit flavors 441), Hexyl acetate develops the strongest and most typical odor in Cox s Orange Pippin apples (279). Hexyl 2-methylbutyrate contributes highly to the flavor of Golden Delicious apples (265). Methyl and ethyl esters of ( )-3-hexenoic, (Z)-4-decenoic (32) and )- and (Z)-4-octenoic acids have some importance in the flavor of pineapple 408). Methyl (Z)-4-decenoate (32) and methyl thiohexanoate account for about 56% of the odor provided by the components of the oxygenated fraction of hop oil 202). Ethyl (jE, Z)-2,4-decadienoate (35) is considered as the character impact compound in the aroma of Bartlett pears (227) (Table 2). The application of this pear ester in reconstitution work has been facilitated by the development of highly stereospecific syntheses 405, 407, 457). Isobutyl an-gelate is considered as an essential constituent of Roman camomile oil 85). 

Ohloff, G., and M. Pawlak Synthesis of Pear Ester , a Novel Synthesis of 2,4-Diolefinic Aldehydes and Esters. Helv. Chim. Acta 56, 1176 (1973). 

A recently developed method for the preparation of (Z)-ap-unsaturated aldehydes, using the phosphorane (122), is effective in the preparation of the pear ester (123) (Scheme 74). ... 

The hydrolysis of as little as 0 5 ml. of the ester can be carried out in the combined reflux-distillation apparatus shown in Fig. 38 (p, 63). Pass a stream of cold water through the vertical condenser. Place in the 10 ml. pear-shaped flask 0 5 ml. of the ester, 5 ml. of 10% NaOH solution and one or two minute fragments of unglazed porcelain and heat the mixture gently for 15 minutes so that the vapours do not rise more than about half-way up the vertical water ondenser. Now run the water out of the ver ical condenser, insert a thermometer at the top, and pass water through the inclined condenser. Heat the flask sufficiently strongly to collect 1--2 ml. of distillate. This is dilute ethanol. 

Amyl Acetate.—This is, with the exception of amyl formate, which is not of practical importance, the simplest possible ester of amyl alcohol, and has the formula CHj. COO. CsHjj. It is a fruity oil, with a strong odour resembling that of the pear, and is known as art ficial oil of pear. It is prepared on a very large scale by, for example, treating 100 parts of dry sodium acetate, 100 parts of amyl alcohol, and 130 parts of sulphuric acid for twelve hours at ordinary temperature, and then distilling off the ester. It has a specific gravity 0-876, and boils at 138°. The alcohol in this ester is not normal amyl alcohol, but isoamyl alcohol. 

The crude ester is cooled, an equal volume of benzene is added, then the free acid is neutralized by shaking with about 250 cc. of a 10 per cent solution of sodium carbonate (Note 4). The benzene solution is poured into 1300 cc. of a saturated solution of sodium bisulfite (about 60 g. of technical sodium bisulfite per 100 cc.), contained in a wide-neck bottle equipped with an efficient stirrer, and the mixture stirred for two and a half hours. The mixture soon warms up a little and becomes semi-solid. It is filtered through a 20-cm. Buchner funnel and carefully washed, first with 200 cc. of a saturated solution of sodium bisulfite, finally with two 150-cc. portions of benzene (Notes 5 and 6). The white pearly flakes of the sodium bisulfite addition product are transferred to a 3-I. round-bottom wide-neck flask equipped with a mechanical stirrer and containing 700 cc. of water, 175 cc. of concentrated sulfuric acid, and 500 cc. of benzene. The flask is heated on a steam bath under a hood, the temperature being kept at 55°, and the mixture is stirred for thirty minutes (Note 7). The solution is then poured into a separatory funnel, the benzene separated and the water layer extracted with a 200-cc. portion of benzene. The combined benzene solution is shaken with excess of 10 per cent sodium carbonate solution to remove free acid and sulfur dioxide (Note 8). The benzene is washed with a little water and then dried over anhydrous potassium carbonate (Note 9). The benzene is distilled at ordinary pressure over a free flame from a 500-cc. Claisen flask, the solution being added from a separatory funnel as fast as the benzene distils. It is advisable to distil the ester under reduced pressure although it can be done under ordinary pressure. The fraction distilling around n8°/5mm., 130710 mm., 138715 mm., 148725 mm., 155735 mm., or... 

Flavanols/Procyanidins Catechin, epicatechin, and their gallic acid esters Apples, grapes, plums, pears, mangoes, okra, peaches, Swiss chard, berry fruits and vegetables in general,... 

The butyl ethanoate produced by Equation (3.30) is an ester, and smells of pear drops. 

Synonyms Acetic acid, amyl ester Acetic acid, pentyl ester AI3-02729 rt-Amyl acetate Amyl acetate Amyl acetic ester Amyl acetic ether /r-Amyl ethanoate Banana oil Birnenoel BRN 1744753 Caswell No. 049A Chlordantoin EPA pesticide chemical code 000169 Holiday pet repellant Holiday repellant dust NSC 7923 Pear oil Pentacetate Pentacetate 28 1-Pentanol acetate 1-Pentyl acetate /3-Pentyl acetate Pentyl acetic ester /3-Pentyl ethanoate Primary amyl acetate UN 1104. 

Synonyms Acetic acid, isopentyl ester Acetic acid, 3-methylbutyl ester AI3-00576 Banana oil BRN 1744750 CCRIS 6051 EINECS 204-662-3 FEMA No. 2055 Isoamyl ethanoate Isopentyl acetate Isopentyl alcohol acetate 3-Methyl-1-butanol acetate 3-Methylbutyl acetate 3-Methyl-1-butyl acetate 3-Methylbutyl ethanoate NSC 9260 Pear oil UN 1104. 

Here are some additional examples of esters as aromas or flavors propyl acetate is the aroma of pears pentyl acetate is the aroma of bananas octyl acetate is that for oranges. 

Synonyms Amyl acetate banana oil pear oil amylacetic ester 3-methyl butyl acetate 3-methyl-1-butanol acetate... 

The flavour of distillates from apple and pear is characterised by typical aroma compounds from these fruits formed by enzymatic degradation of fatty acids to C6-fragments like hexanol, trans-2-hexenol, as well as ethyl esters and acetates of hexanoic acid. In distillates of pears, especially of the variety Bartlett pear, the characteristic pear flavour is mainly dominated by the ethyl and methyl esters of frans-2-czs-4-decadienoic acid and trans-2-trans-A-decadienoic acid [27-29], The biogenesis of these monounsaturated, diunsaturated, and triunsaturated esters may be explained by -oxidation of unsaturated linoleic and linolenic acid in the fruits. The sesquiterpene compound a-farnesene, which is formed during postharvest ripening and storage of Bartlett pears [28], shows that quality and intensity of distilled pear spirits is mainly influenced by the quality and degree of ripeness of the fruits. 

Gatfield et al. [44] reported in 2001 a method to produce natural ethyl E,Z)-2,4-decadienoate, the impact compound of pear. Immobilised lipase from Candida antarctica is capable of transesterifying Stillingia oil in the presence of ethanol. By this process, a complex mixture of ethyl esters is generated. By fractional distillation, the ethyl ester of ( ,Z)-2,4-decadienoate can be isolated from the mixture in a total yield of about 5% and with a high degree of purity. As only... 

Jennings et al (228) fractionated an extract from Bartlett pears into 32 volatile components of which five were found to contribute significantly to the characteristic pear aroma. Later studies indicated that esters of trans-2 cis-4 decadienoic acid and hexyl acetate were significant components of the Bartlett pear aroma (229, 230). More recently, numerous volatiles of Bartlett pears were separated and identified including esters of methyl, ethyl, propyl, butyl, and hexyl alcohols, and Cio to Ci8 fatty acids (231, 232). 

Esters also constitute a group of important flavour compounds. They are the main aroma components found in fruits (apples, pears,. ..). For example, bananas contain 12-18 ppm acetates. The price of the pure flavour compounds, when isolated from fruit, can range between 10,000 and 100,000 US /kg In the past, research has been carried out by our group about the microbial production of fruity esters by the yeast Hansenula mrakii and the fungus Geotrichum penicillatum [10]. A fermentation was developed whereby fusel oil was continuously converted into a mixture of 3-methylbutyl acetate (isoamyl acetate) and 2-methylbutyl acetate, the character impact compounds of banana flavour. 

If the structure of a GA can be inferred from its mass spectrum the suspected compound may be synthesized and its mass spectrum compared with that of the unknown. Thus the structures of GAlj.6 and GA y were confirmed by the partial synthesis of their methyl esters from GA4 (38). This synthesis will be discussed in detail later. GAM was identified in immature seeds of Pyrus communis (pear) in an analogous manner by comparison of its mass spectrum with that of a product obtained from incubating ent-15 -hydroxykaurenoic acid with a mutant of the fungus G. fujikuroi (29). 

Juice of the sand pear can also be converted into vermouth (Joshi et al, 1999). The complete process is illustrated in Fig. 8.3. Dry and sweet versions, with various alcohol levels, have been prepared (Attri et al, 1993). TSS, acidity, aldehyde, phenol, and ester contents increase as a... 

The 1 1 complex b ween bovine serum and an osmate ester is an enantioselective catalyst in the syn hydroxyladon of certain alkenes, although synthetic applications iq>pear to be limited. Asymmetric di-hydroxylation of alkenes is considered in a review on catalytic asymmetric reactions. ... 

Oxidation of alcohols typically proceeds in 4-12 h giving excellent yields of carbonyl products. Chromyl chloride, C1O2CI2, like other Cr species, is a vigorous oxidant of organic compounds. It may be, however, tamed as a silica gel adsoibate. This reagent combination is also a good oxidant of alcohols, alkenes and alkynes, that will tolerate halides, esters, lactones, ethers and nitriles. The shelf life of the reagent t pears to be indefinite in the diy state. 

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