3,328,470 United States Patent Office Patented June 27, 1967 1. 2 3,328,470 GREATER SELECTIVITY IN THE GUERBET As stated, the reaction is carried out at an elevated tem REACTION perature which can lie between about 200 C. and about Ronald L. Poe, Ponca City, Okla., assignor to Continental 300° C. The particular temperature employed will de Oil Company, Ponca City, Okla., a corporation of pend on the alcohol which is being converted, the particu Delaware 5 lar catalyst used and the other operating conditions. Pref No Drawing. Filed Oct. 3, 1963, Ser. No. 313,440 erably, the reaction is carried out in the presence of 16 Claims. (C. 260-642) potassium hydroxide as the catalyst and at a temperature between about 240° C. and 270° C. This invention relates to preparation of alcohols and Pressure is of importance in the process, primarily as particularly to the preparation of 2-branched alcohols by O a means of maintaining the reactants in the desired physi the dimerization of primary alcohols. cal state. Thus, sufficient pressure is employed to main The Guerbet reaction is a reaction which is well-known tain the starting alcohol in the liquid state and this pres to the organic chemist. According to the Guerbet reaction, sure will vary depending on the temperature at which a primary or secondary alcohol which contains a methyl the reaction is carried out. More elevated pressures can ene group attached to the carbon atom of the carbinol be employed if desired, however, they are not ncessary group is condensed with itself (or with another alcohol and where possible, the reaction is ordinarily carried out of the class just described) to form as the principal at atmospheric pressure. product a higher alcohol containing double the number The reaction proceeds readily with the time required of carbon atoms of the starting alcohol, for example, varying inversely with catalyst concentration and tempera n-butanol is condensed to 2-ethylhexanol. Similarly, a 20 ture. Broadly, the reaction time can vary from about 0.1 mixture of n-butanol and ethanol can react to form 2 hour to as high as about 50 hours or higher. Preferably, ethylhexanol (by condensation of two molecules of n however, the reaction is carried out within a time period butanol), n-butanol (by condensation of two molecules of between about 1 and about 8 hours. of ethanol), n-hexanol and 2-ethylbutanol (by condensa A wide variety of alcohols can be converted to the tion of a molecule of n-butanol with a molecule of 25 dimer alcohol within the scope of the invention. In the ethanol). It is also apparent that a certain amount of broad aspect of the invention, these alcohols are defined condensation can occur between the principal higher alco as primary alcohols having at least one hydrogen on the hol product and unreacted starting alcohol, as well as beta carbon atom and can be expressed structurally by between two molecules of the principal higher alcohol the following formula: product, and on up the line, forming a series of higher molecular weight alcohols by condensation which theo 30 retically can involve any two molecules present in the reaction mixture at a given time, if at least one of the two materials undergoing condensation contains a methyl wherein at least one R is hydrogen and at least one R ene group attached to the carbon atom of the carbinol is hydrocarbon, e.g., alkyl, aryl, cycloalkyl, alkaryl and group. 35 aralkyl. While there is no particular limitation on the In the conventional Guerbet reaction, large amounts of number of carbon atoms which can be present in the catalysts are used which have the disadvantage of pro hydrocarbon groups, more usually the alcohols include moting the undersirable reactions, for example, the those containing from 3 to about 20 carbon atoms. Of formation of acid. Conventionally, approximately 33 mole the various types of alcohols which can be used in carry percent catalyst is added to the alcohol to be dimerized. 40 ing out the invention, there are included preferably the It is an object of this invention to provide an improved normal primary alcohols, such as, n-propanol, n-hexanol, process for the dimerization of primary alcohols. n-dodecanol. In addition, the alcohols include the It is another object of this invention to provide an im branched chain primary alcohols, such as, 2-methyl proved process for increasing product selectivity in the butanol, 2 - butyloctanol, 2 - octyldodecanol, 2-methyl dimerization of primary alcohols. 45 octanol and the like; and primary alcohols containing Still another object of this invention is to provide an cyclic Substituents and aromatic substituents, such as, 2 improved process for the dimerization of primary alcohols phenylethanol, 2-benzyloctanol, 2-cyclopentyldodecanol, employing an alkali metal or alkali-metal compound as 2 - cyclohexylphentanol, 2-methylcyclohexylheptanol, 2 the catalyst. benzylpentanol and the like. The foregoing objects are realized broadly by the 50 The catalyst which is employed in effecting the dimeri process of converting primary alcohol having at least one zation reaction is preferably selected from the alkali-metal hydrogen on the beta carbon to 2-branched alcohol in the hydroxides, that is, sodium hydroxide, potassium hy presence of a small amount of an alkali metal or alkali droxide, lithium hydroxide, etc. In addition, the alkali metal compound catalyst. This process is exemplified by metals can also be employed as catalysts and the catalysts the following reaction: 55 also include the alkali-metal alcoholates in which the hy Fr drocarbon portion of the alcoholate corresponds to the - ; H hydrocarbon portion of the alcohol reactant. Sodium hy E.--- droxide and potassium hydroxide are the catalysts which ------ KOH CHg OH -- CEs-CH-CHOH - 60 are more usually employed and of these, potassium hy -------- droxide is preferred. CH-CH-CHOH + H2O The amount of catalyst employed in carrying out the dimerization reaction is important since a high degree of Hg selectivity is obtained only within a relatively narrow In carrying out the process of this invention, the alcohol range of catalyst concentraton. Thus, the amount of cata is contacted with the dimerization catalyst preferably at 65 lyst employed in the practice of the invention must be less an elevated temperature for a period of time sufficient to than 3 mole percent based on the alcohol reactant and convert a substantial portion of the alcohol to the 2 preferably, is not greater than about 2 percent. The cata branched dimer. By appropriately controlling the oper lyst concentration affects not only selectivity but also is ating conditions under which the reaction is carried out a very important factor in the reaction time, with the time and by utilizing an alkali-metal catalyst, it is possible to 70 required decreasing as the catalyst concentration is in obtain selective conversion to the desired dimer alcohol creased. In view of this, it is preferred to use as much in amounts exceeding 90 percent. catalyst as possible, preferably at least 1 percent, however, 3,328,470 4 3 In order to obtain the high degree of selectivity which Smaller amounts of catalyst can effectively be employed, characterizes the process of this invention, it is necessary and any catalytic amount as readily ascertained by those that Water which forms during the dimerization reaction within the skill of the art can be used in carrying out the be removed from contact with the reaction mixture. This invention.Numerous examples could be presented to illustrate 5 can be accomplished in several ways, for example, the specific alcohols and catalysts employed and their conver- Water is readily removed by carrying out the reaction in sion. The following examples are submitted only by way the presence of a dehydrating agent such as calcium hy of illustration and not of limitation, to exemplify various droxide or calcium hydride. Water removal can also be specific aspects of the invention. effected by distillation and which readily occurs with many 10 of the alcohol reactants since the reaction conditions of temperature and pressure are such that water formed in EXAMPLES the reaction is distilled therefrom. In those instances where the reaction conditions are not conducive to the R1 H removal of water, this deficiency can be remedied by Alcohol--------------- R- d -(- OE 5 employment of an azeotrope such as xylene, benzene and Catalyst the like. R3 H The yields which are obtained in the dimerization reac tion will vary depending upon the alcohol reactant, the R1 R2 Rs catalyst and amount thereof and the particular reaction 20 conditions employed. Any alcohol which is not converted H. C1021 C8H17 NaOE in the reaction can be separated from the reaction product EI C6H5CH2 C6H13 K and if desired, recycled to the reaction. The reaction can C2Es be carried out either as a batch process or as a continuous H CH3 Cas CH-C-C-OK process, preferably with recycle of unconverted alcohol. h 25 The following examples are presented in illustration of g-H, the invention. Examples H. C6H11 C3H C6H11 g C-ONa Normal dodecanol was added to a three-necked glass H 30 flask equipped with a stirrer, thermometer and a trap H C6H13 CH KOH attached to a condenser. Potassium hydroxide catalyst H C65 Na was added to the flask and the mixture was heated and C19H21 maintained at an elevated temperature until the reaction H C5Hg C10H1 C.H.-b-c-oNa was complete (distillation of water stopped). The flask h 35 Was then cooled to about 70° C. to 90°. C. and acidified With 25 percent hydrochloric acid. After separation, the H CHg CH KOH organic layer was washed with hot water until a pH of E.