Alkylation with hydrogen fluoride catalyst

The related manufacture of cumene (isopropylbenzene) through the alkylation of benzene with propylene is a further industrially important process, since cumene is used in the synthesis of phenol and acetone. Alkylation with propylene occurs more readily (at lower temperature) with catalysts (but also with hydrogen fluoride and acidic resins) similar to those used with ethylene, as well as with weaker acids, such as supported phosphoric acid (see further discussion in Section 5.5.3). 

When liquid hydrogen fluoride is used as catalyst, alkylation may be accomplished in satisfactory yield (except with ethylene) at room temperatures. Higher temperatures can be used with hydrogen fluoride than with sulfuric acid because it is only with the latter that a side reaction, oxidation of the alkene, must be avoided. 

As in ethylbenzene production, alkylation can be performed either in the gas or in the liquid phase. Propylation of benzene in the liquid phase is achieved with sulfuric acid or aluminum chloride as catalyst at 30 to 40 °C, or with hydrogen fluoride at 50 to 70 °C, and propylene pressures up to 7 bar. The propylene used must be largely free from other olefins. A propylene/propane mixture, such as occurs in refinery gases, can be used for the reaction, since propane is not converted and can readily be stripped from the reaction products. 

The quantity of catalyst necessary may vary considerably. Only catalytic amounts of aluminum chloride required when olefins or alkyl halides are the alkylating agents. - With alcohols or their derivatives, much larger amounts of catalyst are required, owing to inactivation by reaction with the alcohol or with the water formed durii the reaction. With hydrogen fluoride it is universal practice to use a large excess of catalyst, so much so that it is actually the solvent medium for the reaction. 

Chloro-aluminate ionic liquids promote the carbonylation of alkylated aromatic compounds, but fails in the case of oxygenated aromatics. Aldehyde yields of formylation in the acidified neutral ionic liquids were generally similar compared to reactions conducted in HF as solvent/catalyst (cf Table 2.2). The increase in aldehyde yields with the use of extended alkyl chain lengths of the cationic part of the melt, may be due to improved CO solubility. HF/BFs-acidified neutral ionic liquids showed both increases in para-selectivity compared to HF as solvent and catalyst. Formylation of anisole and toluene, but not of phenol in the neutral ionic liquids resulted in increased secondary product formation in comparison with hydrogen fluoride used as solvent/catalyst. This difference in behaviour is not understood at present, but suggests that phenol is a good substrate for formylation in this medium, particularly with the development of a system catalytic with respect to HF/BF3 in mind. 

Prior to 1965, alkylbenzene production was synthesized from petroleum tetrapropylene reacted with an aluminium chloride or hydrogen fluoride catalyst and benzene. The resultant alkylate was a hard branched-chain compound that was considered slowly biodegradable. A straight-chain alkylate, termed LAB (linear alkylbenzene), has been produced since 1965 in the United States. Extensive research has demonstrated biodegradation effectiveness in sewage treatment plants in excess of 95 percent. ... 

Three basic processes have been practiced for linear alkylbenzene manufacture. The most prevalent route of alkylbenzene manufacture is by partial dehydrogenation of paraffins, followed by alkylation of benzene with a mixed olefin/paraffin feedstock, using liquid hydrogen fluoride catalyst. A second route is via partial chlorination of paraffins, followed by alkylation of the chloroparaffin/paraffin feedstock in the presence of an aluminium chloride catalyst. The third process uses partial chlorination, but includes a dehydrochlorination to olefin step prior to alkylation with aluminium chloride or hydrogen fluoride. 

Isopropylnaphthalenes can be prepared readily by the catalytic alkylation of naphthalene with propjiene. 2-lsopropylnaphthalene [2027-17-0] is an important intermediate used in the manufacture of 2-naphthol (see Naphthalenederivatives). The alkylation of naphthalene with propjiene, preferably in an inert solvent at 40—100°C with an aluminum chloride, hydrogen fluoride, or boron trifluoride—phosphoric acid catalyst, gives 90—95% wt % 2-isopropylnaphthalene however, a considerable amount of polyalkylate also is produced. Preferably, the propylation of naphthalene is carried out in the vapor phase in a continuous manner, over a phosphoric acid on kieselguhr catalyst under pressure at ca 220—250°C. The alkylate, which is low in di- and polyisopropylnaphthalenes, then is isomerized by recycling over the same catalyst at 240°C or by using aluminum chloride catalyst at 80°C. After distillation, a product containing >90 wt % 2-isopropylnaphthalene is obtained (47). 

In order to achieve high yields, the reaction usually is conducted by application of high pressure. For laboratory use, the need for high-pressure equipment, together with the toxicity of carbon monoxide, makes that reaction less practicable. The scope of that reaction is limited to benzene, alkyl substituted and certain other electron-rich aromatic compounds. With mono-substituted benzenes, thepara-for-mylated product is formed preferentially. Super-acidic catalysts have been developed, for example generated from trifluoromethanesulfonic acid, hydrogen fluoride and boron trifluoride the application of elevated pressure is then not necessary. 

As a result of alkylation LAB is obtained with a clearly changed composition in comparison with the use of chloroparaffin. With respect to the dialkyl-tetralin content, values are obtained which are comparable to LAB from the HF alkylation process (same olefin base) (Table 11). Another important difference is the 2-phenylalkane content. The isomer distribution depends on the catalyst. The reaction between straight /z-chloroparaffins or n-olefins with benzene in the presence of aluminum chloride leads to the same isomer distribution. In both cases the 2-phenylalkane content is predominant compared to the 3-, 4-, and 5-phenylalkanes. If hydrogen fluoride is used as catalyst the 2-phenylalkane... 

Detal [Detergent alkylation] A process for making detergent alkylate, i.e., alkyl aromatic hydrocarbons such as linear alkyl benzenes, as intermediates for the manufacture of detergents, by reacting C10-C13 olefins with benzene in a fixed bed of an acid catalyst. Developed by UOP and CEPSA as a replacement for their Detergent Alkylate process, which uses liquid hydrogen fluoride as the catalyst. Demonstrated in a pilot plant in 1991 and first commercialized in Canada in 1996. Offered by UOP. 

Xenon difluoride reacts with alkyl iodides at room temperature to give organic derivatives of polyvalent iodine. When an excess of iodomcthane (7) is treated with xenon difluoride it produces a stable solution of methyliodine difluoride in quantitative yield, the use of hydrogen fluoride as a catalyst allows a substantial amount of product to be obtained, while isopropyl iodide decomposes under the action of the reagent.16-21... 

Both aromatic and aliphatic fluoroformates 7 can be readily prepared from phenols or alcohols and carbonyl difluoride and treated with sulfur tetrafluoride without isolation. Hydrogen fluoride evolved in the reaction of hydroxy compounds with carbonyl di fluoride serves as a catalyst for the consecutive reaction with sulfur tetrafluoride.15<)-162 This provides a general, convenient, direct synthesis of aryl and alkyl trifluoromethyl ethers 5 from phenols and alcohols. When the intermediate fluoroformate 7 is isolated prior to treatment with sulfur tetrafluoride, at least one mole equivalent of hydrogen fluoride is necessary to promote the fluorination reaction. 159 163 Representative examples of the conversion of hydroxy compounds 6 into trifluoromethyl ethers 5 via intermediate fluoroformates 7 are given (for other examples 7 -> 5, see Houben-Weyl, Vol. E4, pp 628. 629). 

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