Diolefin reactions

Fig. 3 Undesirable diolefin reactions in alkylation unit. (View this art in color at www.dekker. com.)...

CH = CH — CH = CH — are said to have conjugated double bonds and react somewhat differently from the other diolefins. For instance, bromine or hydrogen is often added so that a product of the type -CHBr-CH=CH-CHBr- is formed. Also, these hydrocarbons participate in the Diels-Alder reaction see diene reactions). They show a tendency to form rubber-like polymers. Hydrocarbons not falling into these two classes are said to have isolated double... 

The reaction of OF2 and various unsaturated fluorocarbons has been examined (35,36) and it is claimed that OF2 can be used to chain-extend fluoropolyenes, convert functional perfluorovinyl groups to acyl fluorides and/or epoxide groups, and act as a monomer for an addition-type copolymerization with diolefins. 

In acetic acid solvent, ethylene gives 1,3-propanediol acetates (46) and propylene gives 1,3-butanediol acetates (47). A similar reaction readily occurs with olefinic alcohols and ethers, diolefins, and mercaptans (48). 

The reaction of dihalocarbenes with isoprene yields exclusively the 1,2- (or 3,4-) addition product, eg, dichlorocarbene CI2C and isoprene react to give l,l-dichloro-2-methyl-2-vinylcyclopropane (63). The evidence for the presence of any 1,4 or much 3,4 addition is inconclusive (64). The cycloaddition reaction of l,l-dichloro-2,2-difluoroethylene to isoprene yields 1,2- and 3,4-cycloaddition products in a ratio of 5.4 1 (65). The main product is l,l-dichloro-2,2-difluoro-3-isopropenylcyclobutane, and the side product is l,l-dichloro-2,2-difluoro-3-methyl-3-vinylcyclobutane. When the dichlorocarbene is generated from CHCl plus aqueous base with a tertiary amine as a phase-transfer catalyst, the addition has a high selectivity that increases (for a series of diolefins) with a decrease in activity (66) (see Catalysis, phase-TRANSFEr). For isoprene, both mono-(l,2-) and diadducts (1,2- and 3,4-) could be obtained in various ratios depending on which amine is used. 

Polymerization of raw feedstock. Aliphatic hydrocarbon resins. Raw feedstock contains straight-chain and cyclic molecules and mono- and diolefins. The most common initiator in the polymerization reaction is AICI3/HCI in xylene. The resinification consists of a two-stage polymerization in a reactor at 45°C and high pressure (10 MPa) for several hours. The resulting solution is treated with water and passed to distillation to obtain the aliphatic hydrocarbon resins. Several aliphatic hydrocarbon resins with different softening points can be adjusted. 

Because the criss-cross cycloaddition reaction is a sequence of two [3+2] cycloaddition steps, the reaction with a,co-diolefins offers a new entry into macro-molecular chemistry New types of polymers with interesting structures and prop erties can be synthesized [213, 214, 215] (equation 48)... 

Paraffins are relatively inactive compared to olefins, diolefins, and aromatics. Few chemicals could be obtained from the direct reaction of paraffins with other reagents. However, these compounds are the precursors for olefins through cracking processes. The C -Cg paraffins and cycloparaffms are especially important for the production of aromatics through reforming. This section reviews some of the physical and chemical properties of C1-C4 paraffins. Long-chain paraffins normally present as mixtures with other hydrocarbon types in different petroleum fractions are discussed later in this chapter. 

Addition polymerization requires a chain reaction in which one monomer molecule adds to a second, then a third and so on to form a macromolecule. Addition polymerization monomers are mainly low molecular-weight olefinic compounds (e.g., ethylene or styrene) or conjugated diolefins (e.g., hutadiene or isoprene). 

The use of light olefins, diolefins, and aromatic-based monomers for producing commercial polymers is dealt with in the last two chapters. Chapter 11 reviews the chemistry involved in the synthesis of polymers, their classification, and their general properties. This book does not discuss the kinetics of polymer reactions. More specialized polymer chemistry texts may be consulted for this purpose. 

Reduction of the catalyst/hydrocarbon time in the riser, coupled with the elimination of post-riser cracking, reduces the saturation of the already produced olefins and allows the refiner to increase the reaction severity. The actions enhance the olefin yields and still operate within the wet gas compressor constraints. Elimination of post-riser residence time (direct connection of the reactor cyclones to the riser) or reducing the temperature in the dilute phase virtually eliminates undesired thermal and nonselective cracking. This reduces dry gas and diolefin yields. 

The catalytic system used in the Pacol process is either platinum or platinum/ rhenium-doped aluminum oxide which is partially poisoned with tin or sulfur and alkalinized with an alkali base. The latter modification of the catalyst system hinders the formation of large quantities of diolefins and aromatics. The activities of the UOP in the area of catalyst development led to the documentation of 29 patents between 1970 and 1987 (Table 6). Contact DeH-5, used between 1970 and 1982, already produced good results. The reaction product consisted of about 90% /z-monoolefins. On account of the not inconsiderable content of byproducts (4% diolefins and 3% aromatics) and the relatively short lifetime, the economics of the contact had to be improved. Each diolefin molecule binds in the alkylation two benzene molecules to form di-phenylalkanes or rearranges with the benzene to indane and tetralin derivatives the aromatics, formed during the dehydrogenation, also rearrange to form undesirable byproducts. 

The LAB production process (process 1) is mainly developed and licensed by UOP. The N-paraffins are partially converted to internal /z-olefins by a catalytic dehydrogenation. The resulting mixture of /z-paraffins and n-olefins is selectively hydrogenated to reduce diolefins and then fed into an alkylation reactor, together with an excess benzene and with concentrated hydrofluoric acid (HF) which acts as the catalyst in a Friedel-Crafts reaction. In successive sections of the plant the HF, benzene, and unconverted /z-paraffins are recovered and recycled to the previous reaction stages. In the final stage of distillation, the LAB is separated from the heavy alkylates. 

For catalysis by Pt(II) and Rh(I) w-olefin complexes (those containing chelating diolefin ligands were less effective), three types of reaction have been observed depending on the nature of the silane (55). 

Of further particular interest was that the crystallographic results on 2,5-DSP and poly-2,5-DSP had pointed out a very important future possibility that an absolute asymmetric synthesis could be achieved if any prochiral molecule, e.g. an unsymmetrical diolefin derivative, could be crystallized into a chiral crystal and if the reaction of the chiral crystal proceeded in the same manner as the 2,5-DSP crystal with retention of the crystal lattice (Wegner, 1972, 1973). Such types of absolute asymmetric synthesis with a high enantiomeric yield have now been performed by topochemical [2+2] photoreaction of unsymmetric diolefin crystals (Addadi etal., 1982 Hasegawa et al., 1990 Chung et al., 1991a,b). 

In this chapter the topochemical [2+2] photoreactions of diolefin crystals are reviewed from the viewpoints of organic photochemistry, analysis of reaction mechanism, and crystallography as well as in terms of synthetic polymer chemistry and polymer physics. 

Recently several examples of diolefin crystals in which the reaction behaviour deviates from the topochemical rule have been observed. For example, in the photoreaction of methyl a-cyano-4-[2-(4-pyridyl)-ethenyljcinnamate (2 OMe), the first reaction occurs exclusively at the pyridyl side although the distance between the ethylenic double bonds on the pyridyl side is exactly the same as that between the ethylenic double bonds on the ester side (4.049 A), as shown in Fig. 5 (Maekawa et al., 1991a). A few other unsymmetrical diolefin compounds display the same regioselective behaviour (Hatada, 1989). 

It is well known that the [2+2] photodimerization of diolefinic compounds is allowed to occur photochemically but not thermally, whereas the cyclobutane cleavage reaction occurs both photochemically and thermally. The cleavage reaction occurs with irradiating light of shorter wavelength... 

On the other hand, the crystallization process of diolefin compounds often plays a significant role in determining their topochemical behaviour, by changing their crystal structure or by forming solvent inclusion complexes. Furthermore, topochemical photoreactions of crystals with )8-type packing are accompanied by thermal processes under moderate control by the reacting crystal lattice (see p. 140). These factors seriously complicate the whole reaction scheme. 

Along with the guidepost (Wegner, 1972, 1973) based on the crystal-to-crystal transition from 2,5-DSP to poly-2,5-DSP, absolute asymmetric synthesis has been achieved by the topochemical reaction of a chiral crystal of an achiral diolefin compound in the absence of any external chiral reagents. 

In the crystal of 1,4-dicinnamoylbenzene (1,4-DCB) (see Fig. 12), the distances between the intermolecular photoadductive carbons are 3.973 and 4.086 A for one cyclobutane ring, and 3.903 and 3.955 A for the other. The two topochemical pathways may occur competitively in a single crystal of 1,4-DCB at the initial stage of reaction. Then, both intramolecular photodimerization and intermolecular photopolymerization of the diolefinic mono-cyclobutane intermediate occur competitively to give tricyclic dimer 21,22,23,24-tetraphenyl-l,4,ll,14-tetraoxo-2(13),12(13-diethanol, [4.4] para-cyclophane or oligomers (Hasegawa et al., (1985). On photoirridation at room temperature the 1,4-DCB crystal gives >90% of the tricylic... 

This is the first example of a topochemical reaction of a molecular complex of a perfectly ordered polymer composite. Complex 2,5-DSP-l OEt is also obtained by simple grinding of homocrystals 2,5-DSP and l OEt, as is observed for the pair of diolefinic compounds described on p. 166. 

Another catalytic application emanating from the Hieber base reaction was developed by Reppe and Vetter [108]. They showed that 1-propanol 126 could be generated by treatment of ethylene 125 with catalytic amounts of Fe(CO)5 78 under CO-pressure and basic reaction conditions (Scheme 33). Thereby, trimethylamine and V-alkylated amino acid derivatives mrned out to be optimal bases for this reaction. Like ethylene 125, propylene could be transferred mainly to 1-butanol diolefins like butadiene only reacted to monoalcohols. By employing these reaction conditions to olefins in the presence of ammonia, primary or secondary amines, mono-, di-, and trialkylamines were obtained whose alkyl chains were elongated with one carbon atom, compared to the olefins. 

It is quite possible that more highly dehydrogented products (e.g. hexadiene or hexatriene) may also be involved in the reaction sequence. However, none of these species was observed in the GLC. This is not surprising since both these species are highly reactive and may not have accumulated to any measurable extent. One could have used labeled diolefins or triolefins in mixture with n-hexane to test this possibility. Although this experiment was not attempted, we would speculate that most of the radioactivity would have been quickly incorporated into the benzene with a small amount perhaps flowing temporarily upstream into the olefins and the paraffin. 

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