United States Patent Office Paterated Mar

3,311,602 United States Patent Office Paterated Mar. 28, 1967 2 aromatic groups with an excess of alkyl chloromethyl 3,311,602 ether in the presence of a halomethylation catalyst, that PROCESS FOR THE CHLOROMETHYLATION OF AROMATIC HYDROCARBONS improved reaction rates, conversions, and yields are ob Charles F. Raley, Jr., Midland, Mich., assignor to The tained under mild conditions with low catalyst concen Doy Chenaica: Company, Midland, Mich., a corpora 5 trations by adding to the chloromethylation reaction mix tion of Delaware ture a catalyst regenerator selected from the group con No Drawing. Filled July 1, 1963, Ser. No. 292,131 sisting of silicon tetrachloride, titanium tetrachloride, ii Ciaims. (C. 260-93.5) sulfur trioxide, oxalyl chloride, phosphorus pentachloride, thionyl chloride and sulfuric acid, in an amount sufficient This invention relates to an improved process for the O to regenerate the catalyst. chloromethylation of aromatic materials with an alkyl To illustrate the unexpected and highly beneficial re chloromethyl ether and catalyst. More particularly, it Sults of this regenerative chloromethylation process, es relates to such a process wherein improved reaction sentially complete monochloromethylation of a linear rates, conversions, and yields are obtained by regenerating polystyrene was obtained in 6 hours at room temperature the activity of the catalyst during chloromethylation. 5 by the addition of 0.5 mole of silicon tetrachloride (SiC) Chloromethylation of aromatic materials to substitute per equivalent of polystyrene to a reaction mixture con a chloromethyl group for a nuclear aromatic hydrogen is taining 5 moles of chloromethyl methyl ether and 0.1 mole an important and versatile synthetic process applicable of zinc chloride per equivalent of polystyrene. Under to many aromatic materials. Process-wise, it convention similar conditions without the addition of SiCl, the con ally involves reaction of the aromatic material either with 20 version to a monochloromethylated product was only 30 formaldehyde and HCl (Eq. 1) or alternately with an percent in 6 hours. Alone SiCl is not an active halo alkyl chloromethyl ether in the presence of a suitable methylation catalyst, but when added to a conventional catalyst (Eq. 2). System as a catalyst regenerator the advantageous results described herein are obtained. The resulting chloro ArH -- HCHO + HCl - ArCH2Cl + H2O (Eq. 1) methyl polystyrene containing an average of 1.00 chloro Catalyst methyl groups per aromatic nucleus is soluble in organic ArH -- ROCH2Cl --> ArCH2Cl -- ROH (Eq.2) Solvents such as toluene and methylene chloride, and With reactive aromatic compounds, the formaldehyde shows no evidence of gelation or appreciable cross-link HCl process is often satisfactory. However, with less 1ng. reactive compounds and particularly with polymeric com 30 Similarly, titanium tetrachloride, sulfur trioxide, oxalyl pounds containing aromatic moieties, such as polystyrene chloride, phosphorus pentachloride, thionyl chloride, and and other vinylaromatic polymers, the alkyl chlorometh Sulfuric acid have been discovered to be effective as yl ether process is usually preferred. catalyst regenerators in this chloromethylation process. in United States Patent 2,694,702, Jones describes the Under standard conditions using a linear polystyrene as chloromethylation of linear vinylaromatic polymers with a test material, addition of one or more of these catalyst chloromethyl methyl ether using a mild Friedel-Crafts regenerators resulted in yields and conversions at least catalyst Such as anhydrous zinc chloride, under con 20 percent greater than those obtained by the usual chlo trolled reaction conditions to give toluene-soluble prod romethyl methyl ether process without causing gelation. ucts having an average of from 0.1 to 1.0 chloromethyl Within this group of additives, SiCl, titanium tetrachlo groups per aromatic nucleus. These chloromethylated 40 ride (TiCl4), and sulfur trioxide (SO3) are particularly polymers are Substantially free of cross-linking and are effective in restoring catalyst activity and hence are gen soluble in organic solvents such as benzene, dioxane, erally preferred. methylene chloride, 1,2-dichloroethane, and chloroform. Many other reagents have been examined such as phos They are highly useful intermediates for the synthesis of phorus oxychloride, phosphorus trichloride, acetal chlo other valuable products such as the water-soluble quat ride, etc. But the efficiency of the indicated catalyst re ernary ammonium derivatives. 45 generators is markedly Superior to that of all other re For many purposes, it is obviously desirable to obtain agents examined. While the reason for this selective ac a high degree of chloromethylation, i.e., a high average tivity is not known, it likely involves the reactivity of the number of chloromethyl groups per aromatic nucleus. reagents with by-product alcohol as well as such other However, in the chloromethylation of linear polystyrene it factors as the stability and solubility of the alcoholysis is in practice difficult to introduce an average of more 50 products. than about 0.85 chloromethyl groups per aromatic nucleus It is believed that the observed decrease in catalyst ac without causing considerable cross-linking and consequent tivity during the reaction is related to the formation of gelation. The more vigorous conditions usually em alcohol (ROH) as a primary by-product of the chloro ployed to achieve a higher degree of chloromethylation, 55 methylation process (cf. Eq. 2). It is known that by such as increased catalyst concentration or reaction tem product alcohol reacts with the alkyl chloromethyl ether perature, also promote cross-linking through further re to form an acetal and HC1. This reaction is, however, action of the substituent chloromethyl groups. reversible and reaches an equilibrium when a sufficient Furthermore, in the Jones process the rate of reaction concentration of HCl develops in the system. Additional is observed to decrease rapidly as chloromethylation pro alcohol then is believed to complex with the catalyst there ceeds. For example, with an essentially linear polystyrene 60 by destroying its catalytic activity. Since the catalyst re having an average molecular weight of about 25,000 and generators are extremely strong alcohol scavengers, they 5 moles of chloromethyl methyl ether and 0.4 mole of are believed to function by removing alcohol from the zinc chloride per equivalent of polystyrene, a 50 percent alcohol-catalyst complex thereby destroying the complex conversion to a monochloromethylated product was ob 65 and regenerating the catalyst. tained in one hour. Conversion thereafter increased to Supporting this rationale is the known fact that this about 63 percent in three hours and to about 72 percent chloromethylation reaction is readily quenched by the ad in six hours. Yet only after 24 hours was a soluble dition of alcohol or other oxygen-containing solvents, such product having an average of 0.85 chloromethyl groups as dioxane, isopropyl ether, tetrahydrofuran, and acetone, per aromatic nucleus obtained. which complex readily with Friedel-Crafts catalysts. Thus It has now been discovered that in the chloromethyla under standard conditions, conversion to monochloro tion of aromatic compounds and polymers containing methylpolystyrene in 4.5 hours is reduced from 27 per 8,811,602 3 4. cent to 19 percent by pretreatment of a zinc chioride cat ether based on the weight of aromatic material, the ex alyst with 1 mole of methanol per mole of zinc and to cess reagent serving as a diluent to maintain a fluid mix less than 6 percent with 2 or more moles of methanol per ture throughout the reaction. Alternately a portion of mole of zinc. Also, it has been observed that bubbling the excess alkyl chloromethyl ether can be replaced by HCl into the chloromethylation reaction mixture destroys another solvent which is resistant to chloromethylation catalyst activity, possibly by reversing the acetal equi such as chloroform, tetrachloroethane, dichloroethylene, librium and thereby increasing the concentration of al or a saturated aliphatic hydrocarbon. cohol. The amount of halomethylation catalyst required in Further support for this mechanism of catalyst regen the improved chioromethylation process varies widely de eration as well as additional evidence of the Surprising O pending upon such factors as the particular catalyst used, effectiveness of this regenerative chloromethylation proc the reactivity of the aromatic material, and the reaction ess was obtained in an experiment with polystyrene in conditions as well as the degree of chloromethylation de which the zinc chloride catalyst was deliberately deac sired. Because the catalyst activity is regenerated during tivated with methanol before addition to the chlorometh the reaction, less catalyst is necessary in the improved ylation mixture. The mixture remained lemon-yellow 15 process. For example, to achieve a high degree of mon in color and essentially no chloromethylation was ob ochloromethylation of polystyrene by the Jones process tained in 24 hours. Then SiC was slowly added and the from 0.2 to 0.5 mole of zinc chloride is required per color changed to orange and then to the deep red typical equivalent of polystyrene. In contrast, high conversions of a reactive chloromethylation. Thereafter the chloro and yields are obtained by the regenerative process here methylation proceeded in normal fashion. 20 in described using from 0.05

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