2-phenyl isomer

The effect of carbon chain length and high vs. low 2-phenyl isomer distribution on viscosity and solubility (cloud/clear point) of a liquid hand dishwashing formulation is shown in Table 5. Two sets of pure LAS homolog samples ranging from Cl0 to Cl3 were prepared. All samples were prepared with pure olefins, but one set was produced with an HF alkylation catalyst (low 2-phenyl) and the other set was alkylated with A1C13 (high 2-phenyl). Each LAB... 

Table 7 gives the apparent CMC and Ksp values for C12 LAS [28]. As carbon chain length increases, the Ksp decreases, which is an indication that the LAS becomes more sensitive to water hardness [27]. It has been reported that the internal phenyl isomers of C,2 LAS are more sensitive to precipitation with Ca2+ than the 2-phenyl isomer [29]. This is presumably due more to the lower CMC of the 2-phenyl LAS isomer than to any increase in the Ksp. 

Dishwashing foam stability performance of an LAS-based light-duty liquid (LDL) is strongly affected by the carbon chain distribution, by water hardness, and, under some conditions, by phenyl isomer distribution. Foaming characteristics of C)2 phenyl isomer blends have been reported previously for conditions where LAS is the single anionic surfactant in the formulation (phosphate-built laundry powder) and the level of residual water hardness is low [30,31]. Under these conditions the internal phenyl isomers of C,2 LAS gave better foam performance than the 2-phenyl isomer. 

Of interest is the relative composition of the LABs, particularly the different amount of 2-phenyl isomer and of nonlinear alkylates, given in Table 8. Branched alkylbenzene (BAB) formed by the AlCl3-catalyzed reaction between propylene, condensed to its tetramer, and benzene are less biodegradable and are termed biologically hard. LABs have to a large extent replaced BABs in the domestic markets because of their improved biodegradability. 

Linear alkylbenzene (LAB) is produced by alkylating benzene with either alkylhalides or mono-olefins, the second option being the most widely used in commercial processes. The characteristics of final LAB, namely the isomer distribution, depend on the alkylation catalyst used HF catalyst produces a LAB known a Low 2-phenyl with a 2-phenyl isomer content around 17%, while fixed bed and A1C13 processes produce a High 2-phenyl LAB, which consists of approximately 30% of this isomer. Commercial LAB is a mixture of Ci0, Cu, C12 and Ci3 homologues with all positional isomers except the terminal one... 

Hydroxybenzo[6]thiophene has been isolated from coal tar.42 It may be prepared from 6-aminobenzo[fr]thiophene by standard procedures.241 6-Methoxybenzo[h]thiophene may be prepared by decarboxylation of the corresponding 2-carboxylic acid,341 and 6-ethoxybenzo[6]thiophene is obtained by reduction of 6-(ethoxy)-thioindoxyl (Section VI, 1,2). 6-Methoxy-5-methylbenzo[6]thiophene is obtained by cyclization of (3-methoxy-4-methylphenylthio)-acetaldehyde dimethyl acetal (Section IV,B).617 The product previously described542 as 6-hydroxy-3-phenylbenzo[6]thiophene has now been shown to be the 2-phenyl isomer.307 6-Methoxy-818 and 6-methoxy-5-methyl-benzo[6]thiophene617 are demethylated by pyridine hydrochloride. 

The chloroparaffin/AlCl3 route is the longest established, but now represents only a minority (-10%) of LAB supply. The product is H2P, with 2-phenyl isomer levels of28-30%. The reaction can be more difficult to control and yields not only a high level of dialkyl tetralin (DAT) impurities, but also high levels of dialkylbenzene and diphenylalkanes. The spent catalyst has to be removed by filtration. 

LAB is often described as high or low 2-phenyl. As already seen, the level of 2-phenyl isomer is determined by the catalyst choice, with low 2-phenyl product made by HF catalyst being dominant. Isomer distribution has a very significant effect on solubility. Figure 4.6 shows how the cloud point (the temperature below which the formulation becomes turbid) varies with LAS type and concentration. 

Linear alkylbenzenes are made from linear terminal olefins and benzene and are important precursors of biodegradable anionic surfactants (LAS, linear alkylbenzenesulfonates). The conventional catalyst is HF, first to be replaced by a fluorinated silica-alumina in the DETAL process. The DETAL process is safer than the HF process and also more cost-effective because no special metallurgy is required and no calcium fluoride waste stream exists.52 Zeolites such as Beta may come to the fore here because they display a higher selectivity to the desired 2-phenyl isomers.55... 

Appearance Water white, clear liquid Specific Gravity 0.86 2-Phenyl Isomer Content 25-35%... 

In the production of linear alkylbenzenes zeolites with ten membered rings yield the desired product, the 2-phenyl isomer, vriiich is the smallest of the isomers, more selectively, but the activity of these zeoUtes is low [98], In a conparative study of several wide pore zeolites it was observed that the selective towards 2-phenyl dodecane in the reaction of dodecene with benzene at 498 K, 0.6 MPa and alkene to benzene ratio of 0.1 decreased in the order H-Mordenite > H-Beta > HY> amorphous silica-ahunina >RE-YwHF. Ahhou the production of the 2-phenyl isomer is desirable in the production of LAB, it is much more inportant to avoid the formation of diphenyl-isomers and branched phenyl isomers. The production of these conpounds can be suppressed by using HY as a catalyst [98,60],... 

In the alkylation of benzene with long-chain a-olefins (Ce, Cg, C12, etc ), the large-pore zeolites mordenite, beta-zeolite, and ZSM-12 favor the less bulky 2-phenyl isomers. HY and rare-earth-Y produce a mixture of other -alkylbenzene isomCTS. Shiqie selectivity is attributed here to both product- and restricted transition state type selectivities [76]. 

Besides the production of cumene and ethylbenzene, there are a number of recent reports on the production of linear alkylbenzene, precursors to detergents, via the alkylation of benzene with C6-C18 olefins. One process uses suspension CD and essentially 100% conversion of olefin at low temperatures of 90-100°C was obtained. An HF-treated mordenite used in the alkylation of benzene and C10-C14 olefins was foimd to give a 74-84% selectivity to linear alkylbenzene containing 80% 2-phenyl isomer. A new patent on the alkylation of aromatic hydrocarbons such as benzene and cumene with straight-chain C6-C20 olefins on acidic catalyst such as zeolites or fluorine-treated zeolite catalyst packed in a Katamax-type packing was granted. A patent application on the manufacture of xylenes from reformate by RD also appeared and higher than equilibrium amounts of para-xylene were claimed. 

The amount and type of LAS in HDLDs depends largely on the physical form of the laundry liquid — unstructured or structured. In unstructured liquids, solubility considerations require the use of smaller carbon chain lengths ( C11). In addition, the choice of cations can also enhance solubility. Potassium and amine cations such as MEA and TEA can be used instead of sodium ions to improve stability [60], An increased ratio of the 2-phenyl isomer in the LAS can also increase solubility [61] and sometimes improve the hardness tolerance of the surfactant [62], In structured liquids, a longer alkyl chain can be more desirable for the formation... 

Reference 6 gave m.p. 276-277° but this was later withdrawn. Reference 6 gave m.p. 228-230° but this was later withdrawn. Possibly the 2-phenyl isomer. 

On the other hand, as found by Borodkin and later confirmed by Rudnev, Bushmelev and Shakirov, the equilibrium mixture of phenyldimethylacenaphthyl-enonium ions is chtnacterized by the predominance of the l,l-dimethyl-2-phenyl isomer (75) ... 

The fourth LAB quality measure is the distribution of phenyl substitution on the alkyl chain, which can influence solubility and viscosity. A higher concentration of the 2-phenyl isomer generally improves the solubility of the resultant LAS surfactant. Much like the concentration of dialkyltetralin present in the LAB, the concentration of the 2-phenyl isomer in the LAB is largely determined by the particular LAB production process. Table 2.1 compares these three additional LAB quality measures as they typically result from the different alkylation processes. 

Particularly, 2-phenyl isomers and dialkyltetralins (DAT) are the components that can be considered as more representative of the adopted alkylation process, as shown in Table 5.2. 

Phenyl isomers content (high values ensure high solubility in water and high viscosity of LAS)... 

The solubility of alkyl-benzene sulphonates increases with decreasing 2-phenyl isomer content. 

The AICI3 process generally produces higher 2-phenyl isomer levels (>25%) than the HF process (<20%). 

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