DE2031921A1 - Isoprene prodn from 3-methyl-3-butene-1-ol - by dehydration in aq acid/salt soln - Google Patents

Abstract

Process for prepn of isoprene (I) from 3-methyl-3-butene-1-ol (II) using as dehydrating agent aq. solns. of acids or substances forming acids in H2O and also their salts, the anion of the acid and salt present being a halogen. Opt. a diluent may be present. Operating temp. at 1 atmos is pref. 60-100 degrees C.

Description

Process for Making Isoprene This invention relates to a new process for the production of isoprene by dehydrating 3-methyl-3-buten-1-ol.

Several processes for the production of isoprene are already known. So one makes the diolefin on a large scale by dehydrogenation of isopentene or Isopentane. It has also been suggested to use isoprene by dimerizing To produce propylene and subsequent methane elimination from methylpentene. Further isoprene can be obtained from isobutene and formaldehyde via the 4,4-dimethyl-1,3-dioxane stage win away. Isoprene can also be obtained by dehydrating 2-methyl-3-buten-2-ol, which can be made from acetone, acetylene and hydrogen obtained. The mentioned Processes are unsatisfactory in many ways. Some are used Raw materials are only available in limited quantities or only in a cumbersome way, the conversion to isoprene is also unselective or not sufficiently high from booty. In addition, there is also insufficient purity of the isoprene produced a deficiency that is particularly evident in polymerizations with organometallic catalysts has a detrimental effect.

It has now been found that isoprene can be obtained by dehydrating 3-Methyl-3-buten-1-ol with acids can be particularly advantageous if you 3-methyl-3-buten-1-ol with the acids or with substances in an aqueous medium Forms acids in the presence of water and salts and optionally of diluents treated, whereby the acids or the acid-forming substances and the salts are so chooses that either the anion of the acid or the anion of the salt or both are involved Are halides substance, which according to the German patent 1,275,049 by Implementation of isobutene and formaldehyde obtainable in a simple and economical manner Isoprene of high purity is technically simple with almost quantitative yield obtain.

It was surprising that isoprene was so excellent after this process Yields is obtained, because it is known from the literature that 3-methyl-3-buten-1-ol both with acids in the liquid phase and in the gas phase via fixed bed catalysts can only be converted into isoprene with great difficulty and with poor yields (cf. Petroleum ahemistry USSR 4 (1965) page 211-220 and J. Orgo Chem. USSR 3 (1968) (8) page 1328). According to these known processes, the reaction is very slow and slow undesirable side reactions, such as hydration and isomerization of 3-methyl-3-buten-1-ol, or decomposition of the alcohol into isobutene and formaldehyde.

The acids used in the new process are monobasic or polybasic inorganic or organic acids suitable which in water have a dissociation constant of at least 1.10-6, such as hydrochloric acid, hydrochloric acid, hydrofluoric acid, Hydrofluoric acid, sulfuric acid, phosphoric acid, formic acid, acetic acid, p-toluenesulfonic acid, Trichloroacetic acid, oxalic acid, maleic acid or ion exchange resins, the sulfonic acid groups contain.

Substances that form acids in an aqueous medium are e.g. B.

Aluminum trichloride, boron trifluoride, titanium tetrachloride or acyl halides like acetyl chloride.

Mixtures of the acids and / or the acid-releasing substances can also be used use. For economic reasons, one will use the cheaper ones directly Prefer acids.

Since the process according to the invention is carried out in the presence of water, the acids are expediently used from the outset as aqueous solutions. The concentration of the aqueous acids can fluctuate within wide limits and lies Preferably between 0.01 and 40 percent by weight Senr strong @@@@@@@@@@@@@@@@@@@@@@@@@ association constants from more than 101, will be advantageous in concentrations of 0.01 up to 20, in particular 0.05 to 10 percent by weight and acids with smaller dissociation constants than 10, advantageously in concentrations of 1 to 40, preferably 5 to 30 percent by weight used. However, the method is also outside the limits specified here Acid concentrations executable.

In general, lower temperatures are used when higher temperatures are used Prefer acid concentrations and vice versa. For example, it can be expedient be, with a temperature increase of z. B, 30 cc the acid concentration by the factor 0.2 to 0.1 decrease.

Suitable salts come into consideration which are soluble in water and which are derived from Derive acids as defined above. This means that the salts of Derive acids with a dissociation constant of at least 1.10-6. The selection of the Salt is to be made so that in cases where no hydrohalic acid is used, a salt is taken, which is different from a hydrohalic acid derives. Suitable salts are, for example, sodium chloride, potassium bromide, calcium iodide, Sodium sulfate, sodium phosphate, calcium chloride, aluminum sulfate, magnesium sulfate, Zinc chloride and sodium oxalate.

Since you can use all salts with about the same success - so far they are combined with the appropriate acidity - become economic considerations suggest the use of cheap saline such as table salt, calcium chloride or Glauber's salt. Mixtures of the Salse can also be used. For example, is sea water a suitable medium to carry out the reaction.

The concentration of the salts in the aqueous dehydration medium is limit upwards by their solubility at the reaction temperature. However, this upper limit can also be exceeded in order to dilute the solution to counteract this with the water produced during dehydration. As the reaction speed decreases with increasing dilution, the salt content in the aqueous-acidic medium should Do not fall below 3 percent by weight, although dehydration in this area as well accelerated by a factor of more than 100 compared to the absence of salts is.

The dehydration is carried out according to the new method, for. B.

at temperatures up to 140 00. It is advisable to choose temperatures which at least correspond to the boiling point of isoprene. These are when working under Normal pressure, for example, temperatures between 40 and 100 00. Will be reduced or elevated pressure worked, the temperature range can be z. B. to 0 to Move 140 ° C. The rate of reaction is naturally increased by lowering the temperature decreased. Since increases in temperature above 100 ° adversely affect the yield noticeably the reaction is preferably carried out at normal pressure between 60 and 100.degree before.

To increase the yield, it is advantageous in many cases to use diluents to be added to the conversion mixture. Diluents are within the scope of this invention liquid organic compounds inert under the conditions of dehydration, which expediently boil in the temperature range in which the dehydration is carried out. For example, the following may be mentioned as diluents: hydrocarbons such as gasoline fractions in the boiling range from 50 to 120 ° C, benzene, toluene, xylene, cyclohexane and methylcyclohexane. Adding these diluents in amounts of 5 to 100 percent by weight has proven useful, absorbed in the acidic saline solution.

The new process for the production of isoprene can be discontinuous are executed. However, it is advantageous to do it continuously. After a 3-methyl-5-buten-1-ol is particularly useful continuous procedure into the charged with the acidic aqueous salt solution and to the reaction temperature Brought reaction vessel given with stirring to the extent in which the formed Remove isoprene from a fractionating column attached to the top of the rectification vessel can be. The water released during dehydration is also used continuously-removed from the acidic salt solution, for example by distillation. A consumption of the residual aqueous salt solution in the reaction vessel existing catalyst does not occur or only to a small extent.

Isoprene is an important monomer for the production of polymers as well as a valuable intermediate z. B for the manufacture of terpinen.

The parts mentioned in the example are parts by weight. You behave to parts by volume like kilograms to liters.

Example We obtained the results given in the table in the following experimental set-up: a cylindrical reaction vessel equipped with a stirrer with a content of 4 parts by volume is mixed with the acidic salt solution, which you pass through Mixing salt, acid and water produces, charged. The mixture is heated with stirring to 90 to 95 00. The reaction vessel is operated at 40 to 45 oO Provided reflux condenser and an attached descending condenser, in where the isoprene formed is condensed. In experiment no. 8, in addition to the acidic Saline solution still used 0.5 parts by volume of methylcyclohexane.

Experiment No. 9 is a comparative experiment in which in the absence is worked by salt.

3-Methyl-3-buten-1-ol becomes continuous in the specified period admitted. After completion of the supply of methylbutenol, the The reaction was held at the reaction temperature for a further 2 hours. The amount of the resulting Isoprene, which on average already has a purity of 94 to 96 ffi and contains only a little methylbutenol which was not condensed in the dephlegmator, was gas chromatographed certainly, Table Comp. Vol. Parts Parts Methylbutenol Parts Parts Such parts acid salt parts added isoprene heavier no water ben in boiling Hours of by-products 1 0.6 0.007 0.3 1 3 0.72 0.1 Hydrochloric acid CaCl2 35% strength 2 0.6 0.04 p-To- 0.3 1 2 0.70 0.12 luolaulfonic acid CaCl2 acid 3 1.2 0.2 oxalic 0.6 5 10 3.7 0.4 acid NaCl 4 1.2 0.68 phosphoric acid 0.4 4 12 2.9 0.3 phosphoric acid NaCl 85% 5 1.2 0.06 Hydrochloric acid 0.5 2 3 1.5 0.15 acid NH4Cl 35% 6 1.2 0.36 0.4 4 1 9 6 1.2 0.36 hydrochloric acid Na3PO4 35 94ig 7 1.2 0.08 Shos- 0.4 2 8 1.5 0.15 phosphoric acid NaBr 85% ig 8 1 0.06 Phosphoric acid 0.8 5 11 3.8 0.43 phosphoric acid NaCl 85% 9 0.6 0.007 hydrochloric acid - 1 3 0.001 35% 10 0.5 0.01 hydrochloric 0.25 1 8 0.74 0.05 acid 35% NH4Cl 11 1.0 0.02 boron 0.5 2 15 1.45 0.12 fluoride-NaCl etherate BF3.

O (C2H5) 2 12 0.6 0.4 Eia- 0.3 0.425 20 0.31 0.025 vinegar NaCl

Claims (2)

Claims 1. Process for the production of isoprene by dehydration of 3-methyl-3-buten-1-ol with acids, characterized in that the 3-methyl-3-buten-1-ol with the acids or with substances that form acids in the aqueous medium in the presence treated by water and salts and optionally by diluents, wherein the acids or the acid-forming substances and the salts are chosen so that either the anion of the acid or the anion of the salt or both anions are halides. 2. The method according to claim 1, characterized in that the Dehydration at temperatures up to 140 ° C., preferably between 60 and 10000, undertakes.