Branched alkanes synthesis

Linepithema humile reveals an additional pattern of qualitative differences. Reproductive queens up-regulate the synthesis of hydrocarbons of intermediate chain length (de Biseau et al., 2004). In workers, additional components in the short- and long-chain areas (13-methylpentacosane and di- and trimethyl-branched alkanes with chain lengths of 33 to 37) are present as well. Linepithema also produces large colonies, and workers are sterile. 

Nevertheless, thermodynamic reversibility may prove a disadvantage in particular systems. A classic example is provided by the synthesis of individual rotax-anes ( bead on a thread compounds), discussed in detail in Chapter 4. After threading of the macrocyclic bead on to an open-chain component by self-assembly, it has been found desirable to block the reverse (unthreading) pathway by subsequent covalent attachment of branched alkane groups to each end of the thread so that any tendency for separation of the components is blocked. That is, the final covalent step is equivalent to tying a knot in each end of the thread to stop the bead from slipping off. 

The separation of linear and branched alkanes is also of importance in the process known as dewaxing, in which the removal of normal alkanes makes the product hydrocarbon less viscous and reduces the so-called pour point temperature. Such processes can be combined with catalytic isomerisations to optimise the value of oil fractions (Chapter 8). Linear paraffins are also separated using a zeolite-based process from kerosene fractions to give reactants for the synthesis of linear alkylbenzene sulfonate anionic surfactants, which are both cost effective and biodegradable. 

The differences in hydrocarbon patterns in surface waxes and in the components of interior tissue are illustrated by analysis of pupae of Manduca (tobacco hornworm). n-Alkanes only comprised ca 3% of the hydrocarbon fraction of the cuticular wax, the balance being unsaturated compounds. In contrast, internal tissues (fat bodies, muscle, gut) contained the same carbon spectrum (C21 to C41) as in the wax but now branched alkanes made up the bulk of the hydrocarbon fraction ca 80%), followed by n-alkanes (9%) with the residue being unsaturated compounds The proportion of n-alkanes in the hydrocarbon fraction from cuticular wax of a Bombyx silkworm fell from 95 to 35% on passage from the larval to the pupal stage " and similar results have been found for Trichoplusia (cabbage looper) and Drosophilia (fruitfly) species. However, it is likely that the cuticular wax has a more stable composition over the adult life of most insects and is only synthesized at (low) rates sufficient to replace that lost by wear and tear. The site of synthesis has been demonstrated to be in the cuticle in a cockroach species no hydrocarbon synthesis occurred in preparations from fat bodies . 

The Fischer-Tropsch synthesis, which may be broadly defined as the reductive polymerization of carbon monoxide, can be schematically represented as shown in Eq. (1). The CHO products in Eq. (1) are any organic molecules containing carbon, hydrogen, and oxygen which are stable under the reaction conditions employed in the synthesis. With most heterogeneous catalysts the primary products of the reaction are straight-chain alkanes, while the secondary products include branched-chain hydrocarbons, alkenes, alcohols, aldehydes, and carboxylic acids. The distribution of the various products depends on both the type of catalyst and the reaction conditions employed (4). 

The RP-Cis LC separation of this mixture of aliphatic linear alkane sulfonates (CnH2n+i—SO3) and SAS from an industrial blend in combination with APCI—LC—MS(—) detection is presented as total ion mass trace (Fig. 2.11.2(f)) together with selected mass traces (m/z 277, 291, 305 and 319 for (re +x = 11-14)) in Fig. 2.11.2(b)-(e), respectively. The resolved mass traces proved the presence of large number of isomers of every SAS homologue in this blend. This complexity is generated because of the linear isomer precursor and the mixture of branched alkyl precursor compounds applied to chemical synthesis [22], In parallel to elution behaviour observed in GC the branched isomers of alkylsulfates in LC separation were expected to elute first. 

Refineries and petrochemical industry Paraffins, olefins, acetylenes, reformer gas, hydrocracking gas, solvents Sweetening of liquid petrol gas and aromatics, removal of CO2 from olefin containing gases, purification of synthesis gas Normal and branched-chain alkanes... 

Exercise 22-23 Show explicitly how an alkyl side chain of alkylbenzenesulfonates could be formed with a quaternary carbon, if the C12 alkane used at the start of the synthesis contained any branched-chain C12 isomers. 

Figure 8.3 Synthetic routes and useful chiral synthons for synthesis of the enantiomers of alkanes with a single methyl branch.

Lehmler, H.-J., Bergosh, R.G., Meier, M.S. and Carlson, R.M.K. (2002). A novel synthesis of branched high-molecular-weight (C40+) long-chain alkanes. Biosci. Biotech. Biochem., 66, 523-531. 

It is noteworthy that in the study of A. cocke relli (Smith etal, 2009), synthetic n-alkanes were used, while in other studies usually branched or unsaturated alkanes were synthesized. However, standard synthesis of such compounds leads to a mixture of stereoisomers. If social insects can differentiate between these stereoisomers, bioassays with such synthetic compounds may lead to artifacts. An important future goal is to assess the importance of such stereoisomers and test the respective natural form in the bioassays. 

The basic sources of petrochemical synthesis are benzene and its homologues. The production of these compounds from petroleum is profitable. In 1996, the world requirements for benzene will grow up to 24-26 million tons per year. Non-oxidizing dehydrogenation of alkanes is a subject of intensive investigation. So, the selection and increase of the assortment of highly effective catalysts for the synthesis of olefins and aromatic hydrocarbons from alkanes are very important for development of this branch of industry. There are three main catalysts for non-oxidized dehydrogenation ... 

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