Branched-chain dimers

BF,-Fl20-alkanoic acids 1-hexene, 1-decene, 1-tetradecene high branched-chain dimers to pentamers 909, 910... 

Dimerization of butadiene with organometallic cobalt 7i-complexes, such as ( t-C3H5)3Co, (1,5-cycle CgH 12)2 0, or [Co(CO)2(C4He)]2, gives branched chain dimers in good yields, equation (7-9). An intermediate complex isolated from the reaction is probably involved, equation (7-10). 

Propjiene (qv) [115-07-1] is the predominant 0x0 process olefin feedstock. Ethylene (qv) [74-85-1J, as well as a wide variety of terminal, internal, and mixed olefin streams, are also hydroformylated commercially. Branched-chain olefins include octenes, nonenes, and dodecenes from fractionation of oligomers of C —C olefins as well as octenes from dimerization and codimerization of isobutylene and 1- and 2-butenes (see Butylenes). 

Another alternative method to produce sebacic acid iavolves a four-step process. First, butadiene [106-99-0] is oxycarbonylated to methyl pentadienoate which is then dimerized, usiag a palladium catalyst, to give a triply unsaturated dimethyl sebacate iatermediate. This unsaturated iatermediate is hydrogenated to dimethyl sebacate which can be hydrolyzed to sebacic acid. Small amounts of branched chain isomers are removed through solvent crystallizations giving sebacic acid purities of greater than 98% (66). 

Currently, there is continuing work on an iadustry standard method for the direct determination of monomer, dimer, and trimer acids. Urea adduction (of the methyl esters) has been suggested as a means of determining monomer ia distilled dimer (74). The method is tedious and the nonadductiag branched-chain monomer is recovered with the polymeric fraction. A micro sublimation procedure was developed as an improvement on urea adduction for estimation of the polymer fraction. Incomplete removal of monomer esters or loss of dimer duriag distillation can lead to error (75). 

J. D. Mercer and L. L. Nesbit. Oil-base drilhng fluid comprising branched chain paraffins such as the dimer of 1-decene. Patent US 5096883,1992. 

The cyclodimerization depicted in Scheme 7.19 is one of the many examples concerning cation-radicals in the synthesis and reactions of cyclobutanes. An authoritative review by Bauld (2005) considers the problem in detail. Dimerization is attained through the addition of an olefin cation-radical to an olefin in its neutral form one chain ends by a one-electron reduction of the cyclic dimer cation-radical. Unreacted phenylvinyl ether acts as a one-electron donor and the transformation continues. Up to 500 units fall per one cation-radical. The reaction has an order of 0.5 and 1.5 with respect to the initiator and monomer, respectively (Bauld et al. 1987). Such orders are usual for branched-chain reactions. In this case, cyclodimerization involves the following steps ... 

Of conrse, the cyclic cation-radical formed should be less stable than the alkene cation-radical (which contains a double bond that is favorable for the spin-charge scattering). However, the cation-radical product and corresponding nentral species are generated in a concerted process. The process involves simultaneous covalent bond formation and one-electron reduction of the cyclic product (Karki et al. 1997). Similar to other branched-chain processes, the cation-radical dimerization is characterized by an activation enthalpy that is not too high. These magnitudes are below 20 kJ mol for the pair of cyclohexadiene and trani-anethole (p-MeOCgH4CH=CHCHMe, Z-form Lorenz and Bauld 1987). It is clear that the cation-radical variant of cyclodimerization differs in its admirable kinetic relief. For cyclohexadiene and tran -anethole, catalytic factors are 10 and 10, respectively (Bauld et al. 1987). 

The primary reactions in the alkylation of isobutane produce octanes from butylenes, heptanes from propylene, and nonanes from amylenes. Also, when dimer and trimer polymers of isobutylene are used with isobutane, the polymer is broken down during the reaction, and the resulting products are branched chain octanes similar to those produced when isobutylene is charged. Sulfuric acid consumption is somewhat higher for the diisobutylenes, however, and there are more side reactions than for isobutylene. 

A number of different dimers and ohgomers are produced from fatty acids and alcohols. These are branched-chain compounds with significantly lower melting points than straight chain structures of similar molecular weight. Fully saturated dimers... 

Dimerization is well known to be a side reaction in the Chichibabin reaction (78RCR1042). In fact, dimerization can be the only product with certain alkylpyridines (79USP4177349 81USP4267335). Under normal Chichibabin conditions, heating a heterogeneous mixture of sodium amide in a hydrocarbon at atmospheric pressure with a branched chain alkylpyridine leads to... 

Terpenoids are widespread natural products that are formed from C5 isoprene units leading to their characteristic branched chain structure. Terpenoids are divided into families on the basis of the number of isoprene units from which they are formed. Thus there are monoterpenoids (Cio), sesquiterpenoids (C15) diterpenoids (C20), sesterterpenoids (C25), triterpenoids (C30) and carotenoids (C40). The isoprene units are normally linked together in a head-to-tail manner. However, the C30 triterpenoids and C40 carotenoids are formed by the dimerization of two Ci5 and C20 units, respectively. Hence, in these cases the central isoprene units are linked in a head-to-head manner. The presence of tertiary centres in the isoprenoid backbone of the terpenoids facilitates skeletal rearrangements in the biosynthesis of these natural products. As a consequence, on first inspection some structures appear not to obey the isoprene rule. 

The aldolization mentioned was subsequently used461 for an interesting synthesis of branched-chain sugars. Thus, on reaction with formaldehyde, 78 gives, stereospecifically, 1,6-anhydro-3-C-(hydro xy-methyl)-2,3-0-isopropylidene-/3-D-(yxo-hexopyranos-4-ulose, which subsequently undergoes reduction at C-4 by a crossed Cannizzaro reaction leading to l,6-anhydro-3-C-(hydroxymethyl)-2,3-0-isopropyl-idene-/3-D-talopyranose. On the other hand, an attempt to condense 78 with ethyl formate did not result in the expected 3-C-formyl derivative only the dimer 88 was obtained.461... 

The product of photplysis of thebainequinol, previously reported to be a dimer,has been shown by X-ray studies to have the structure (131). Branched chain alcohols in the 6,14-endo-ethanotetrahydrothebaine series of structure (132 R = Me or H) are readily rearranged by formic acid to tetra-hydrofurans (133), which are further transformed by mineral acid into the bases (134) with the loss of the elements of water.These acid-catalysed rearrangements differ markedly from those previously reported for unbranched alcohols. ... 

It seems clearly established that volatilization is a free radical process initiated at chain ends transfer is responsible for the formation of dimer, trimer, etc. The mechanism of main chain scission is less clear. It seems nevertheless probable that weak links associated with peroxy structures in the chain are present in the polymers prepared by free radical mechanism. They would break very rapidly at the onset of heating. Further chain scission is probably due to random breaking of the chain. This random breaking is accelerated if head-to-head, branch chains or main chain unsaturation are present. Transfer occurs but is not very important. 

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