Branched carboxylic acids

The reaction of trivalent carbocations with carbon monoxide giving acyl cations is the key step in the well-known and industrially used Koch-Haaf reaction of preparing branched carboxylic acids from al-kenes or alcohols. For example, in this way, isobutylene or tert-hutyi alcohol is converted into pivalic acid. In contrast, based on the superacidic activation of electrophiles leading the superelectrophiles (see Chapter 12), we found it possible to formylate isoalkanes to aldehydes, which subsequently rearrange to their corresponding branched ketones. 

These are effective high-octane gasoline additive oxygenates. The conversion of isobutane into isopropyl, methyl ketone, or isopentane into isobutyl, methyl ketone is illustrative. In this reaction, no branched carboxylic acids (Koch products) are formed. 

The hydrocarboxylation of an olefin, catalyzed by strong mineralic acids (Koch-Haaf reaction), leads to branched carboxylic acids [57] ... 

Nicolas, E., Russell, K. C., and Hruby, V. J. (1993). Asymmetric 1,4-addition of organo-cuprates to chiral a, b-unsaturated N-Acyl-4-phenyl-2-oxazolidinones A new approach to the synthesis of chiral b-branched carboxylic acids. J. Org. Chem. 58, 766—770. 

The asymmetric synthesis of / -branched carboxylic acid derivatives was accomplished by conjugate addition of mixed organoaluminum reagents to optically active Arabinose-derived c -unsaturated A-acyloxazolidinones (Scheme 47). Efficient stereocontrol was achieved using different optically active bicyclic oxazolidinones, yielding (.R)- or ( -configured / -branched carboxylic acid derivatives.136a... 

These reactions are notable because a-branched carboxylic acids usually do not undergo efficient Kolbe coupling. Similarly, Kubota et al. have achieved highly efficient homo and crossed coupling reactions using trifluoromethylated carboxylic acids as shown in Scheme 7.7 [77,78]. Notably, the protection of the hydroxy group of the acids 12 is not necessary. 

The coupling reactions are in general limited to primary carboxylic acids (RCH2CO2H). a-Branched carboxylic acids lead to non-Kolbe products. However, carboxylic acid (74) with the electron-attracting trifluoromethyl group in the a-position yields the Kolbe coupling product (75) (Scheme 26) [99,100]. 

Other chemical studies did not find sex or seasonal differences in the composition of mammalian scents. No sex differences in the composition of mixtures of volatile compounds from glands have been found in the brushtailed possum, Trichosurus vulpecula, for example. The same profiles of low-molecular-weight branched carboxylic acids were found in paracloacal gland secretions of males and females (Woolhouse etal., 1994). Branched carboxylic acids also occurred in the preorbital gland secretion of a female sika deer [Ccrvus nippon) (Wood, 2004). Comparisons between the compositions of secretions in different, related species permit assumptions about functional adaptations and possible evolutionary pathways. Such comparisons are available for five Mustek species (Brinck etal., 1983), and three species of hyenas (Buglass etal., 1990). 

The newer HFC refrigerants are not soluble in or miscible with mineral oils or alkylbenzenes. The leading candidates for use with HFC refrigerants are polyol ester lubricants. These lubricants are derived from a reaction between an alcohol and a normal or branched carboxylic acid. The most common alcohols used are pentaerythritol, trimethylolpropane, neopentylglycol, and glycerol. The acids are usually selected to give the correct viscosity and fluidity at low temperatures. 

For increased solubility to prevent bloom, shorter-chain carboxylic acids or zinc carboxylates can be substituted. The use of chain-branched carboxylic acids reduces the tendency for the formulations to lose sulfur cross-links or revert upon prolonged heating (7). Translucent articles such as crepe soles can use a zinc carboxylate or employ zinc carbonate as a transparent zinc oxide. 

Explain why highly branched carboxylic acids such as... 

J. Goossen of the Max-Planck-Institut, Muhlheim, has found Chem. Commun. 2004,724) that in situ activation of the acid with phthalic anhydride and inclusion of the bis phosphine DPE-Phos substantially slow alkene isomerization, which can be essentially eliminated by running the reaction to only 80% conversion. Both linear and branched carboxylic acids work well. 

Highly selective transformation of terminal acetylenes to either linear or branched carboxylic acids or esters may be achieved by appropriately selected catalyst systems. Branched esters are formed with high selectivity when the acetylenes are reacted with 1-butanol by the catalyst system Pd(dba)2/PPh3/TsOH (dba = dibenzylideneacetone) or palladium complexes containing PPh3. Pd(acac)2 in combination with various N- and O-containing phosphines and methanesulfonic acid is also an efficient catalyst for the alkoxycarbonylation of 1-alkynes to yield the branched product with almost complete selectivity.307,308... 

Under appropriate conditions, Mn(0 Ac)3 can be used as a free-radical initiator for the homolytic iddition of acetic anhydride to terminal alkenes. Linear or a-branched carboxylic acids can be jroduced in 70-80% yields based on a-alkenes.507... 

The extent of decarboxylation primarily depends on temperature, pressure, and the stability of the incipient R- radical. The more stable the R- radical, the faster and more extensive the decarboxylation. With many diacyl peroxides, decarboxylation and oxygen—oxygen bond scission occur simultaneously in the transition state. Acyloxy radicals are known to form initially only from diacetyl peroxide and from dibenzoyl peroxides (because of the relative instabilities of the corresponding methyl and phenyl radicals formed upon decarboxylation). Diacyl peroxides derived from non-CC-branched carboxylic acids, eg, dilauroyl peroxide, may also initially form acyloxy radical pairs however, these acyloxy radicals decarboxylate very rapidly and the initiating radicals are expected to be alkyl radicals. Diacyl peroxides are also susceptible to induced decompositions ... 

The homochiral f -branched carboxylic acids (13 or enf-13 Table 1) have been used for the synthesis of a variety of natural products21 such as California red scale pheromone,14 a-skytanthine,22 the southern com rootworm pheromone,15 and norpectinatone.16 Pure (5)-3-trichloromethylbutyric acid (a structural subunit of some sponge metabolites) was prepared via conjugate addition of ClaCMgCl to the chiral cro-tonate (16) followed by hydrolysis (Scheme S).23... 

Similarly, Lippmaa and coworkers evaluated the relative acidities of linear and branched carboxylic acids from the variation with degree of protonation of the measured 13C NMR shifts.23 The method was then extended to secondary deuterium IEs, evaluated from the variation with degree of protonation of the measured 13C NMR shifts of a mixture of isotopologues.24 The data were fit by nonlinear least squares to Equation (17), where 6H and 6D are the observed chemical shifts of undeuterated and deuterated isotopologues, 6H and <5d are those chemical shifts in the deprotonated form, < >]) and are those chemical shifts in the protonated form, R = K /K, and n is the degree of protonation of the undeuterated material. This is the same equation as Equation (15), but adapted to deuteration, and again n is evaluated from chemical shifts as (hH — <5h)/(<5h - h)-... 

Vinyl acetate is polymerized in aqueous emulsion and used widely in surface coating and in adhesives. Copolymerized with vinyl esters of branched carboxylic acids and small quantities of acrylic acid, it gives paint latices of excellent performance characteristics. G. C. Vegter found that a coagulum-free latex of very low residual monomer content can be produced from a mixture of an anionic and a nonionic emulsifier according to a specific operating procedure. The freeze/thaw stability of polymeric latices has been investigated by H. Naidus and R. Hanzes. 

Emulsion Copolymerization of Vinyl Esters of Branched Carboxylic Acids with Vinyl Acetate... 

Three highly useful synthetic transformations are presented in this section the synthesis of isoflavones from chalcones, the synthesis of a-arylalkanones fmm arylalkenes, and the synthesis of a-arylalkanoic acids from aryl ketones. Two others are potentially useful methods, but are not as yet widely used the preparation of a-branched carboxylic acids from a ynes, and the ring expansion and ring contraction of cyclic alkenes and ketones. 

The formyl cation HCO+ (vco at 2110 cm ) is generated from CO under pressure in the presence of HF/SbFs. Concentrated sulfuric acid or the HCl/CuCl system, activates carbon monoxide toward the electrophilic attack on aromatic hydrocarbons to form aromatic aldehydes (Gatterman-Koch reaction). Branched carboxylic acids are obtained from alkenes and CO in the presence of concentrated sulfuric acid (Koch process) (equation 3). ... 

Pantothenate (also designated vitamin B5, 64, Fig. 7) is biosynthesized de novo in plants and many microorganisms but must be obtained from nutritional sources by animals (20, 34). The branched carboxylic acid 63 is obtained from a-ketoisovalerate (61), which is an intermediate of valine biosynthesis, via 62. P-Alanine (60) is obtained by decarboxylation of aspartate (54) in microorganisms. Plants and yeasts can biosynthesize P-alanine from spermine (58) (35). An additional pathway to 60 starting from uracil (59) has been reported in plants,where... 

Racemic or achiral a-azido acids are synthesized by direct azide substitution on commercially available a-bromo carboxylic acids or by radical bromination of carboxylic acids followed by azide substitution. In general, azido acids are stored in the dark to avoid photolytic degradation with loss of nitrogen temperatures above 50 °C should be avoided. Radical a-bromination of a-branched carboxylic acids as required for the synthesis of a,a-dialkyl or a,a-diaryl amino acids is performed with A-bromosuccinimide. This is followed by nucleophilic substitution with sodium azide or other azide donors, e.g. tetrabutylannmonium azide, to produce achiral or racemic a-azido-a,a-diaIkyl or a-azido-a,a-diaryl carboxylic acids (Scheme 74).Synthesis of more sterically hindered a,a-disubstituted azido acids leads to hydroxy compounds when prolonged reaction times are required and not sufficient care is taken to operate under dry conditions and an inert atmosphere.t ... 

Potassium manganate, K2Mn04, purple crystals similar to potassium permanganate [529], forms a dark-green aqueous solution [830]. It is prepared from potassium permanganate and potassium hydroxide at 100 °C [830] or 120-140 °C [529]. Its use is limited to the syn hydroxylation of double bonds [529] and the hydroxylation of tertiary carbons in branched carboxylic acids [830, 557]. It offers no advantages over potassium permanganate. 

The resulting diastereomers of P-branched carboxylic acid derivatives 180 and 181 could be separated by chromatography or crystallization. The pure diastereomer 182 was cleaved from the carbohydrate auxiliary by treatment with Li0H/H202 furnishing the (7 )-configured carboxylic acid 183 (Scheme 10.60). The oxazolidinone 178 was recovered almost quantitatively in this process. 

---