Trans acids

Ethyl chrysanthemate (ethyl 2,2-dimethyl-3 c and t -[2-methylpropenyl]-cyclopropane carboxylate) [97-41-6] M 196.3, b 98-102 /llmm, 117-121 /20mm. Purified by vacuum distn. The free trans-acid has m 54° (from, EtOAc) and the free cis-acid has m 113-116° (from EtOAc). The 4-nitrophenyl ester has m 44-45° (from pet ether) [Campbell and Harper J Chem Soc 283 1945 IR Allen et al. JOrg Chem 21 29 1957]. 

Chrysanthemum dicarboxylic acid or pyrethric acid may exist in eight stereoisomers, owing to the trans or cis configuration on the side chain of the double bond as well as that of the cyclopropane. The natural acid has been shown to be the trans-trans acid. As in the case of the chrysanthemum monocarboxylic acid, the naturally occurring configuration is more insecticidally active than the racemic form or any of the three isomers synthesized. 

Hogeveen138 measured apparent acidity constants of substituted /i-phenylthio-, /J-phenylsulfinyl- and / -phenylsulfonyl-acrylic acids (cis and trans) in 50% v/v ethanol. The p values for transmission through SCH=CH, SOCH=CH and S02CH=CH were 0.531, 0.389 and 0.320 respectively for the cis acids and 0.652, 0.282 and 0.331 for the trans acids. These results were discussed in considerable detail and compared with those of pertinent related systems. Little importance was attached to the small differences between p values for cis/trans isomers, and the relative transmissions were taken as the mean p values 0.59,0.34 and 0.33. The superior transmission of SCH=CH was attributed to greater polarizability. The values for pKJtrans) — pKJcis) of isomeric acids were also discussed. For the sulfonyl acids this is almost constant at 0.1 unit for the sulfinyl adds there is some variation about a mean value of 0.26 unit, and for the thio adds there is also some variation about a mean value of — 0.15 unit. The differing behavior of the three systems in this respect was explained in terms of hypothetical conformations and electrostatic interactions therein. 

Decarboxylation of (44) on heating gave a mixture of < ts and trans acids (39) which were separated by chromatography. Each was converted to the phenyl ketone (38). 

The free trans-acid has m 54° (from, EtOAc) and the free cis-acid has m 113-116° (from EtOAc). The 4-... 

It is interesting to note that although cis-trans isomerism about the double bond is theoretically possible in cinnamic acid, the Perkin reaction gives rise only to the traits form, m.p. 133°, the cis form, m.p. 68° (termed aWo-cinnamic acid) being unstable and easily converted into the trans acid. 

Barbano and Sherbon (1975) decided that the distribution of fatty acids in the high melting fractions of milk fat supported the hypothesis that at least a portion of these TGs were synthesized via the MG pathway. Trans acids were found in the fractions, indicating that these acids behave as saturates. 

Smith et al. (1978) have described a procedure for the GLC determination of cis and trans isomers of unsaturated fatty acids in butter after fractionation of the saturated, monoenoic, dienoic, and polyenoic fatty acid methyl esters by argentation TLC. Total trans acids were much higher, as measured by infrared spectrophotometry than by GLC, probably because some of the acids could have two or more of the trans bonds designated as isolated by infrared spectrophotometry. Enzymatic evaluation of methylene-interrupted cis, cis double bonds by lipoxidase resulted in lower values than those obtained by GLC. The authors mention that the lipoxidase method is difficult, requiring considerable skill, and suggest that their method is suitable for the determination of the principal fatty acids in complex food lipids such as bovine milk fat. 

The presence of trans isomers in partially hydrogenated food fats has aroused concern (Emken 1983). If present, trans, trans 18 2 would dilute EFA activity, as the acid must have the cis, cis configuration and the trans, trans acid does affect several enzymes involved in the... 

Aqueous alkali hydrolyzes lactones and the products, e.g. (287), are frequently unstable or recyclize, depending on other substituents present. Coumarin is hydrolyzed by dilute alkali first to the yellow cis acid (coumarinic acid) salt (288) which recyclizes to coumarin on acidification but when heated with alkali isomerizes to the trans acid (coumaric acid) salt (289). When it is desirable to identify the hydrolytic product of such a reaction it is better to incorporate a methylating agent so that the reverse reaction cannot then occur. Hot aqueous alkali converts methyl 3-bromocoumalate (290) into furan-2,4-dicarboxylic acid (73JCS(Pl)ll30). 

Further support for the intermolecular route is provided by the isolation of the substituted trans-cinnamic acid, the normal Perkin product. This arises through elimination of carboxylic acid from the fully acylated species (393) rather than cyclization. For example, a considerable amount of 2-acetoxy-3-methoxycinnamic acid is formed from 3-methoxysalicylaldehyde, perhaps as a result of steric interference with cyclization so allowing the intermolecular process to predominate (39JPR(152)23). It should be noted that trans- 2-hydroxycinnamic acids do not cyclize under normal Perkin conditions, though the cis isomer does so quite readily. Isomerization of the trans acid has been effected by treatment with a trace of iodine in acetic anhydride or by UV irradiation. 

Exercise 18-51 The c/s- and frans-butenedioic acids give the same anhydride on heating, but the trans acid must be heated to much higher temperatures than the c/s acid to achieve anhydride formation, Explain, Write a reasonable mechanism for both reactions,... 

Attachment of a crotonate chain to the alcohol (78), through a mixed carbonate ester, sets up the intramolecular Diels-Alder reaction in the synthesis of podophylotoxin.111 The starting benzocyclobutenol (78) was procured by the sequence of steps shown in Scheme 16. A similar route using a carboxylic ester, in place of the nitrile (76), for the benzyne cyclization gave a mixture of cis- and fra/u-benzocyclo-butenes but ester hydrolysis led to the pure trans acid (77).112... 

Bowden94 studied the transmission of substituent effects through C=C in the esterification of 3-substituted acrylic acids with diazodiphenylmethane (DDM) and in the ionization of the same acids. The ap values of the substituents were used to characterize their electronic effects for Hammett-type correlations. In esterification with DDM at 30 °C, the p values of the trans acids and the cis acids were 1.682 and 1.772, respectively, in ethanol... 

Cyclopropanone cleavage with elimination 72 can also lead to ring contraction as in the synthesis of the trans acid 74 from natural pulegone13 70. Bromination gives the unstable dibromide 71 that is immediately treated with ethoxide to initiate the Favorskii rearrangement. The product is a mixture of cis and trans isomers of the ester 73 but hydrolysis under vigorous conditions (reflux in aqueous ethanol) epimerises the ester centre and gives exclusively the trans acid 74. 

A mixture of potassium fluoride (33.83 g, 0.582 mol), 2,4 -dibromoacetophenone (80.93 g, 0.291 mol), and DMF (350 ml) was stirred at room temperature for 5 min. A solution of 4 1 mixture of (cis trans) acids (45.0 g, 0.265 mol) in DMF (50 ml) was then added to the reaction mixture and the whole stirred at room temperature for 3 h, then at 100°C for 30 min. The reaction mixture was cooled to room temperature and diluted with H20 (200 ml). The aqueous solution was extracted with Et20 (4x400 ml). The combined ethereal extracts were washed with H20 (3x400 ml) and dried over sodium sulfate. After the solvent was partially removed in vacuo, a precipitate was formed. The slurry was the filtered to give 51.0 g (53%) of p-bromophenacyl ester of 6-ethyl-5-methyl-3,6-dihydro-2H-pyran-2-carboxylic acids as a white solid material, melting point 137°-138°C. 

The importance of recrystallization to the progress of a reaction was demonstrated again in the solid-state photoreactivity of o-methoxycinnamic acid (24). Cis-o-methoxycinnamic acid (cis-24), when crystallized and irradiated at room temperature, gives rise to the cis and trans acids and to trans/trans dimers (25), as shown in Scheme 18. When the reaction is carried out at low temperature, how-... 

The actual function of aconitic acid in the plant physiology is not clearly understood. Cis-aconitic acid undoubtedly is present to a certain extent in the plant because of its role in the citric acid cycle but the factors which cause the accumulation of comparatively large quantities of aconitic acid have not been clearly defined. Whether the concentration of aconitic acid which is formed in the plant is the cts-form exclusively or is a mixture of the cis- and the trans- acids is also unknown. Balch, Broeg and Ambler,37 in their investigations, reported considerable variation in the aconitic acid content of various crusher juices of Louisiana... 

Fatty acid composition. High temperature processes can cause formation of trans-acids, particularly of trans-octadecenoic acids. The levels are quite small, but can be detected by GC on suitable columns (BPX70, CpSil88, etc.). Of particular relevance is the fact that these, once formed,... 

Offer, N.W., Marsden, M., Dixon, J., Speake, B.K. and Thacker, F.E. (1999) Effect of dietary fat supplements on levels of n-3 polyunsaturated fatty acids, trans acids and conjugated linolenic acid in bovine milk. Animal Sci., 69, 613—625. 

This structure has two chiral centres, so how will we know which diastereoisomer we have The answer was simple the stereochemistry has to be tram because Feist s acid is chiral it can be resolved (see later in this chapter) into two enantiomers, Now, the cis diacid would have a plane of symmetry, and so would be achiral—it would be a meso compound, The trans acid on the other hand is chiral— it has only an axis of symmetry. If you do not see this, try superimposing it on its mirror image. You will find that you cannot. 

Over nickel catalysts, aromatic carboxylic acids can be hydrogenated without difficulty as their sodium salts. Thus, e>-179 and m-toluic acids,180 m-hydroxybenzoic acid,181 and tetrephthalic acid182 were hydrogenated to the corresponding saturated acids in high yields over Raney Ni at elevated temperatures and pressures. Examples are shown in eqs. 11.47 and 11.48. o-Toluic acid and terephthalic acid afforded the trans acids predominantly under these conditions. 

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