Pivalic acid, formation from

Also in non-cyclic, branched hydrocarbons cleavage of the carbon chain may occur under formation of carbonium ions, e. g. by depolymerization and disproportionation, as discussed in the previous chapter. Thus, under suitable reaction conditions diisobutylene may yield 2 moles of pivalic acid. Aside from cracking of C-C bonds, carbonium ions may also be obtained from paraffins by hydride transfer. 

According to the above reaction scheme the carbonylation reaction has to be carried out in two steps In the absence of water the olefin is first converted at 20-80°C and 20-100 bar by the aid of mineralic acid and carbon monoxide into an acyliumion. In a second step the acyliumion reacts with water to the carboxylic acid. The mineral acid catalyst is recovered and can be recycled. The formation of tertiary carboxylic acids (carboxylic acids of the pivalic acid type) is enhanced by rising temperature and decreasing CO pressure in the first step of the reaction. Only tertiary carboxylic acids are formed from olefins that have at the same C atom a branching and a double bond (isobutylene-type olefins). 

Koenig and Wolf (1967) reported a similarly small value of 1.195 (=1.02 per D) for the formation of t-butyl radical from the perester of pivalic acid (reaction (41)). 

Different immobilization methods were applied for Jacobsen s catalyst. The entrapment of the organometallic complex in the supercages of the dealuminated zeolite was achieved without noticeable loss of activity and selectivity. The immobilized catalysts were reusable and did not leach. For the oxidation of (-)-a-pinene the system used only O2 at RT instead of sodium hypochloride at 0 °C. There was a disadvantage in the use of pivalic aldehyde for oxygen transformation via the corresponding peracid. This results in the formation of pivalic acid, which has to be separated from the reaction mixture. 

Homoadamantanes.—The benzene-photosensitized polar addition of acetic acid or pivalic acid to 4-homoadamantene (763) gave 2,4-dehydrohomoadamantane (764) and either the esters (765) and (767) or the esters (766) and (768). The products are obtained from the 4-homoadamantyl cation, a proton source being essential to the formation of (764) in AcOD the resulting (764) and (765) both contained onedeuterium atom in the expected positions. Diazotization of 4-homoadamantylamine in AcOH yielded (763), (764), and (767) which is in contrast to the products of buffered acetolysis of 4-homoadamantyl tosylate, namely (763) and (767). A vibrationally excited form of the 4-homoadamantyl cation in the photosensitized addition and in the diazotization reaction accounts for the observations except that it is not clear why compounds (765) or (766) are formed only in the photochemical reactions. 

The oxidation of a ( )-flavanone with Tl(ni) nitrate, Pb tetracetate, phenyliodonium diacetate (PIDA), or [hydroxyl(tosyloxy)iodo]benzene in trimethyl orthofonnate affords the corresponding ( )-2,3-dihydrobenzo[h]furan derivative as a major product. The structures, including the relative stereochemistry, and a plausible mechanism of formation are reported. The preferred formation of a flavone from the ( )-flavanone by PIDA is explained by quantum-chemical calculations on the intermediate formed by the addition of this reagent to the enol ether derivative of the ( )-flavanone." Formation of mixed anhydrides by rapid oxidation of aldehydes, activated by pivalic acid, Bu OCl in presence of pyridine and MeCN is catalysed by TEMPO (2,2,6,6-tetramethylpiperidin-l-oxyl). The anhydrides can be converted in situ to esters, secondary, tertiary or Weinreb amides in high yield. Oxidation of the aldehyde to 2-propyl esters is also possible using only catalytic amounts of pivalic acid." ... 

The fact that 31 is a four carbon chain in which every carbon bears a substituent, three of them oxygen and one a methyl group, suggests R,R-tartaric acid as a logical precursor (15.16). Scheme 4 outlines an extraordinarily efficient route from R,R-tartaric acid to 31 in an overall yield of 64%. Correlation of 31 via cuprate coupling and selective formation of the pivalate at the secondary alcohol gives 32 which was previously derived from 29. 

Reduction of carboxylic acids to aldehydes can be carried out via in situ formation of acid anhydrides by the treatment of carboxylic acids 155 with an excess of pivalic anhydride (146). The acylpalladium intermediate, prepared in this way, is hydrogenolyzed to give aldehyde 156. Separation of the Asired aldehyde 156 from other byproducts is tedious under these conditions [61,66]. 

Some lactones can polymerize in the presence of compounds like alcohols, amines, and carboxylic acids without additional catalysts. The reactions, however, are slow and yield only low molecular weight polymers Exceptions are polymerizations of pivalolactone in the presence of cyclic amines that yield high molecular weight polyesters at high conversion. The initiating steps result from formations of adducts, amine-pivalate betaines ... 

Two synthetic approaches have been prevalent in the preparation of these dinuclear coupled complexes. The first involves the reaction between a dimetal tetracarboxy-late and a bridging ligand that contains two active protons such as a dicarboxylic acid. This has been extensively used by the Chisholm group in the synthesis of dimers of dimers, compounds of type I [7,8], In reactions of this type the formation of the dimer of dimers is achieved by its preferential precipitation from solution. The most simple example of this type of reaction is seen in the reactions of oxalic acid with the dimetal pivalates shown in (2) (M = Mo or W). 

The reaction proceeds via the formation of a first chiral zwitterionic intermediate from pivalic anhydride and the amidine-based catalyst. A mixed anhydride is then generated in the presence of the racemic carboxylic acid and activated by the chiral acyl-transfer catalyst to form the second zwitterionic intermediate. The latter species selectively reacts with a nucleophilic alcohol to afford the desired enantioenriched carboxylic ester (Scheme 41.10). 

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