United States Patent 0 C6 Patented Jan
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3,227,740 United States Patent 0 C6 Patented Jan. 4, 1966 1 2 mercially available diols are the various Pluronics manu 3,227,740 factured by Wyandotte Chemicals. PREPARATION OF ALKYL CARBONATES Various polyols can also be used alone or in admix— Donald M. Fenton, Anaheim, Calif., assignor to Union 011 Company of California, Los Angeles, Calif., a cor ture with any of the aforementioned alkanols and glycols poration of California to impart cross-linking to the polymer. Examples of suit No Drawing. Filed Feb. 25, 1963, Ser. No. 260,844 able polyols are the various triols such as: glycerol, penta 13 Claims. (Cl. 260—463) glycerol, erythritol, pentaerythritol, adonitol, arabitol, hexanhexol, etc. Alkylene oxides, e.g., propylene and This invention relates to a method for the prepara ethylene oxide, can be condensed on any of the afore tion of dialkyl carbonates which are Useful for a variety mentioned polyols to provide high molecular weight re of purposes including solvents, and poly(alkylcarbonates) actants. Examples of such are the polyoxyethylene glyc useful as plasticizers, oils, etc. erol ether, polyoxypropylene glycerol ether, etc. An I have found that such dialkyl carbonates and polycar other suitable high molecular weight polyol is commercial bonates can be readily prepared by the reaction of an al ly available in the Tetronic series of Wyandotte Chemi kanol or polyol and carbon monoxide in the presence of 15 cals. These tetraols comprise blocks of polymers of a solution of mercuric salts in an organic solvent. The propylene and ethylene oxides and are prepared by con crude reaction products comprise the alkyl carbonate or densing propylene oxide on an alkylene diamine and poly(alkyl carbonate), mercury and the acid correspond thereafter condensing ethylene oxide on the intermediate ing to the anion, of the mercuric salt employed. The di product. Products having molecular Weights from about alkyl carbonate or poly(alkyl carbonate) is readily re 1000 to 10,000 or more are available in this series. covered from the crude reaction product and the remain Preferably, the polyols are used in combination with ing materials subjected to known oxidizing conditions to glycols and/ or monohydroxyl reactants to limit the degree oxidize the mercury to the mercuric salt for recycling of cross-linking and thereby permit facile recovery of the to the reactor. product in accordance with conventional practice in the The reaction is operated at relatively mild conditions, 25 alkyd polymer art. e.g., temperatures between about 30° and about 300° C. The reaction medium can be any organic solvent which and pressures from atmospheric to about 500 atmos is liquid at the reaction conditions and which is inert to pheres. While the presence of slight amounts of water the reactants, i.e., inert to carbonates, carbon monoxide, can be tolerated, the yields are decreased in its presence mercury salts and/or alcohol. The particular alcohol and, therefore, the reaction is preferably conducted under employed as a reactant can be used in excess and thus anhydrous conditions. comprise the reaction solvent. This is the preferred em The reactant alcohol can be any desired primary al bodiment since it simpli?es the product recovery steps. If cohol corresponding to the particular alkyl carbonate to desired, however, other organic solvents can be employed be synthesized. Generally, alicyclic and aliphatic primary including various ethers such as: methyl ethyl ether, di monohydroxy alcohols having from 1 to about 25 car 35 ethyl ether, diisopropyl ether, dichloroethyl ether, ethyl bons can be employed to prepare the dialkyl carbonates, ene glycol diisoamyl ether, ethylbenzyl ether, diethylene e.g., methanol, ethanol, propanol, butanol, isobutanol, glycol diethyl ether, triethylene glycol diethyl ether, tetra amyl alcohol, isoamyl alcohol, hexanol, isohexanol, cyclo ethylene glycol dirnethyl ether, etc. hexanol, heptanol, isoheptanol, cycloheptanol, 3-methyl Various esters can also be employed as the solvent, hexanol-l, lauryl alcohol, 3,4-diethylheptanol-l, 4-ethy1 40 e.g., methyl formate, ethyl formate, methyl acetate, ethyl cyclohexanol, etc. Preferably, low molecular weight al acetate, n-propyl formate, isopropyl acetate, ethyl propio cohols having 1 to about 6 carbons are used. nate, n-butyl for-mate, sec-butyl acetate, isob-utyl acetate, The dialkyl carbonate prepared corresponds to the al ethyl n-butylate, n-butyl acetate, isoamyl acetate, n-amyl kyl group of the particular alcohol employed, thus the use acetate, glycol diformate, furfurol acetate, isoamyl n of methanol results in the production of dimethyl car 45 butyrate, ethyl acetyl acetate, diethyl oxalate, glycol di bonate, ethanol to diethyl carbonate, propanol to dipropyl acetate, isoamyl isovalerate, methyl benzoate, ethyl ben carbonate, butanol to dibutyl carbonate, cyclohexanol to zoate, methyl salicylate, n-propyl benzoate, n-butyl dicyclohexyl carbonate, etc. Mixtures of two or more oxalate, etc. alcohols yield corresponding carbonates, e.g., methanol The saturated hydrocarbons can of course be used as 50 and ethanol when employed as the reactants yield a mix a suitable inert solvent, e.g., pentane, hexane, heptane, ture of dimethyl carbonate, diethyl carbonate, and meth octane, decane, ‘dodecane, benzene, toluene, xylene, yl ethyl carbonate, etc. kerosene, etc. The poly(alkylcarbonate) products are prepared by sub The mercuric salts which can be employed are those jecting a glycol or aliphatic polyol to the hereindescribed soluble in the reaction medium. Included in such salts reaction conditions. Glycols yield generally linear poly .are the mercuric halides and the carboxylates of the mers whereas the various polyols yield, of course, cross lower molecular weight carboxylic acids, e.g., mercuric linked polymers having a diversity of properties. To chloride, mercuric bromide, mercuric ?uoride, mercuric illustrate, any of the following glycols can be used as acetate, mercuric formate, mercuric propionate, mercuric reactants: ethylene glycol, trimethylene glycol, 1,2-pro 60 butyrate, mercuric pentonate, etc. Of these, mercuric pylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, acetate is preferred. tetramethylene glycol, pentamethylene glycol, 1,2-pentyl The reaction is believed to proceed through two steps, ene glycol, 1,3-pentylene glycol, hexamethylene glycol, and is exempli?ed by the following: 1,2-hexylene glycol, 1,3-hexylene glycol, 1,4-hexylene gly col, dipropylene glycol, carbitol, glycerol methyl ether, 0 glycerol ethyl ether, diethylene glycol, etc. 65 The poly(alkylene oxide) polymers can also be em ployed as a convenient source of glycols. Particularly useful are polyoxyethylene, polyoxypropylene, as well as block polymers of ethylene oxide and propylene oxide. wherein: These diols are commercially available in a variety of X represents the particular anion of the mercuric salt, forms and degrees of polymerization. Examples of com e.g., the aforementioned halide or carboxyl groups. 3,227,740 3 4;» As previously mentioned, the preferred embodiment Example 2 comprises the use of mercuric acetate with the resultant Dimethyl carbonate was prepared in the same appara production of acetic acid in the crude reaction product. tus by the reaction of 100 milliliters methanol, 32 grams The reaction can be performed in a single step by mercuric acetate and 21 milliliters toluene as a solvent. introducing the reactants, i.e., carbon monoxide, the alco The bomb was pressured to 400 p.s.i.g. with carbon hol and mercuric salt into a reaction zone at the desired monoxide, heated, with rocking, to 50° C. for one hour, temperature, about 150° to about 350° C. and desired then 100° C. for one hour and ?nally, 200° C. for two pressures from about 10 to about 1000 p.s.i.g. Preferably hours. After cooling, the pressure returned to 300 p.s.i.g. temperatures from about 200° to about 250° C. and pros The ‘bomb was opened and contained 20 grams of mer sures from 50 to about 500 p.s.i.g. are used. 10 cury and a yellow-green liquid which was added to 100 Because mercuric salts are reactive with alcohols at milliliters water. The organic phase Was distilled and a elevated temperatures, it is preferred to perform the re high yield of dimethyl carbonate was recovered there action in separate steps. In the ?rst step, the solution is from. treated to saturation with carbon monoxide and the Example 3 alcoholic or organic solution of the resultant mercuric 15 carbonate is thereafter heated to the necessary reactive The 20 grams mercury from Example 2 was added to temperature to form the dialkyl carbonate or poly(alkyl 150 milliliters acetic acid containing 2 milliliters concen carbonate). In this manner the competing reaction be trated nitric acid. Air was introduced into the mixture tween the alcohol and the mercuric salt is avoided and the and a white solid immediately was formed. The mix— desired carbonate formation is favored. 20 ture was heated and at 80° C. (1 hour later) the maxi In general, temperatures between about 0° and about mum amount of white solid had formed and the metallic 100° C. can be used in the ?rst step to absorb carbon mercury had disappeared. Further heating to 105° C. monoxide; preferably temperatures from about 25° to dissolved the white solid and a clear solution was left. about 75° C. are used. High pressures are preferred Upon cooling, a white precipitate formed which was to favor absorption of carbon monoxide, generally pres 25 ?ltered to obtain 27 grams mercuric acetate which can be sures from about 10 to about 1000 p.s.i.g. can be used, used in repeated reactions for the formation of dialkyl preferably between about 100 and about 500 p.s.i.g. are carbonates. used. Example 4 The length of the primary carbon monoxide absorption 30 A poly(hexamethylenecarbonate) was prepared by con step depends on the degree of contacting achieved be densing 12 grams of hexamethylene glycol in 100 milli tween the liquid and gas.