Highly branched carboxylic

Explain why highly branched carboxylic acids such as... 

Versatic acids are highly branched carboxylic acids made by Shell. Versatic is a trade name, not a chemical name. 

One of the most common early uses of the Favorskii rearrangement was for the preparation of highly branched carboxylic acids and esters. For instance, when 3-bromo-3-methyl-2-butanone is treated with sodium isopropoxide at room temperature, isopropyl trimethylacetate is generated in 64% yield. ... 

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. 

Highly Branched Acids. These acids, called neoacids, are produced from highly branched olefins, carbon monoxide, and an acid catalyst such as sulfuric acid, hydrogen fluoride, or boron trifluoride. 2,2,2-Trimethylacetic acid (pivaUc acid) is made from isobutylene and neodecanoic acid is produced from propylene trimer (see Carboxylic Acids, trialkylacetic acids). 

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. 

One of the first hyperbranched polymers described in the literature was polyphenylenes, which were presented by Kim et al. [30-32] who also coined the term hyperbranched . The polyphenylenes were prepared via Pd(0) or Ni(II) catalyzed coupling reactions of various dihalophenyl derivatives such as di-bromophenylboronic acid. The polymers were highly branched polyphenylenes with terminal bromine groups which could be further transformed into a variety of structures such as methylol, lithiate, or carboxylate (Fig. 5). 

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... 

Another practical limitation of esterification reactions is steric hindrance. If either the acid or the alcohol participants possesses highly branched groups, the positions of equilibrium are less favorable and the rates of esterification are slow. In general, the ease of esterification for alcohols, ROH, by the mechanism described is primary R > secondary R > tertiary R with a given carboxylic acid. 

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. 

Lactones are normally stable compounds, which have found ample application as synthetic intermediates, and, quite recently, have been detected as the central structural unit in physiologically active natural products like obaflorin (123) and lipstatin (124). Characteristic applications of 3-lactones in synthesis are the stereospecific CO2 elimination to form di- and tri-substituted alkenes (e.g. from 125 equation 40) or Grignard addition to the carbonyl group e.g. equation 41). Particularly useful is the formation of 3-lactone enolates (126), which react with a variety of electrophiles (EX) wiA high stereocontrol (equation 42). Organocuprates may be used in chain elongations to form 3-branched carboxylic acids (equation 43). ... 

Fulvic acids. Marine sedimentary humic substances soluble in base and acid (fulvic acids) have previously been examined by and NMR (12). The dominant structural components were postulated to be polysaccharide - like substances, probably polyuronic acids. Solid-state NMR spectra of fulvic acids isolated from a number of marine and estuarine sediments are shown in Figure 1. Major peaks at 72 and 106 ppm betray the overwhelming presence of polysaccharide -like substances, and, as shown by Hatcher and others (12.), the moderate peak for carboxyl or amide carbon at 175 ppm suggests that these polysaccharides are more like polyuronides. Aromatic carbons (110 to 160 ppm) are decidedly minor components. Aliphatic carbons (0-50 ppm) are also minor components. H NMR spectra shown by Hatcher and others (12) indicate that these aliphatic structures are highly branched. 

Humic acids of marine and estuarine sediments are characterized by major amounts of paraffinic structures that previous studies have shown to be highly branched and to contain significant quantities of carboxyl/amide and alcohol/ether carbon. Some humic acids, namely those from well preserved sapropelic marine sediments show significant quantities of carbohydrate-like structures incorporated. This, no doubt, is a reflection of the solubility characteristics of polysaccharides which may have some carboxyl functionalities (uronic acid groups). 

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