DE1022222B - Process for the preparation of 1,8-diisocyan-p-menthane - Google Patents

Description

Process for the preparation of 1,8-diisocyan-p-menthane The invention relates to the preparation of 1,8-diisocyan-p-menthane of the formula after a good and cheap method, according to which a suitable carbamate in the presence of a basic catalyst, e.g. B. of a water-soluble metal hydroxide or alcoholate or of water-insoluble metal oxides or hydroxides, is thermally decomposed. This thermal decomposition can be carried out in various ways.

The vapors of the carbamate can be passed through a pipe that contains the basic Connection contains.

Preferably, however, the carbamate is heated to its boiling point in the presence of the basic compound and the diisocyanate is obtained by distillation. The implementation proceeds according to the following scheme: CH3 CH3 C NHCOOR 'CN = C - O CH2 CH2 heat CH2 CH2 > II + 2R'OH CH CH basic CH CH 2 2 catalytic converter 2 CH CH C-NHCOOR 'CN = C = O CH3 CH3 CH3 CH3 R 'denotes any hydrocarbon radical which, however, may be at most benzene unsaturated, such as a saturated aliphatic group such as diethyl or ethyl, a saturated alicyclic group such as the cyclohexyl radical, or an araliphatic group such as benzyl.

However, it is best to use starting materials with a lower one Alkyl group, such as methyl, ethyl, propyl or butyl, so that together with the diisocyanate the resulting alcohol can easily be separated off from this by distillation.

In US Pat. No. 2,407,712 it has already been suggested Carbamates containing a primary alkyl group, e.g. B. an n-butyl or n-dodecyl group, contained on the nitrogen atom by simply heating into the corresponding. Transfer isocyanates. However, such a method is not suitable for production of 1,8-diisocyanp -menthan because these carbamates of p-menthane are surprisingly heat resistant and can be distilled without decomposition. The vessel of the invention is only implemented in the presence of a basic compound instead of.

In the Ber. German chem. Ges., Vol. 41, 1908, pp. 4184-85 the conversion of Na urethane into Na isocyanate is described. This reaction is however also unsuitable for the production of 1,8-diisocyan-p-menthane, as they result Participation of the alkaline catalyst in the conversion only to an inorganic one Salt leads.

Beilstein's handbook of organ. Chemie, Vol. III, 4th edition, P. 32 (main work, 1921) and p. 25 (supplementary work II, 1942), cannot be used for production of 1,8-diisocyan-p-menthane are used. Here is also only the Formation of K- and Na-Isocya, described nat.

General processes for the preparation of organic diisocyanates are indeed in Liebigs Annalen der Chemie, Vol. 562, 1949, pp. 75 to 136, treated. However, it cannot be done by any of the procedures specified there, not even after the » Carbonate-Phosgene Process «, the diisocyanate prepared according to the invention obtained will.

The basic catalyst used can be water-soluble or water-insoluble be. If it is water soluble, it must be at least as basic as sodium acetate be, d. In other words, as a 0.1N aqueous solution, it must have a p-value of at least 250 at 250 8, better between 10 and 13. Suitable compounds are the oxides and hydroxides and alcoholates of the alkali metals, such as sodium hydroxide, sodium methylate, lithium oxide or potassium ethylate, as well as the salts of alkali metals with weak acids, especially with aliphatic carboxylic acids, e.g. B.

Sodium acetate, also potassium carbonate and lithium carbonate alkali metals, z. B. sodium and potassium can also be used, in particular because they form alcoholates with the alcohols formed during the process, which are among the best catalysts of the present process.

Alkaline earth oxides and hydroxides can also be used, e.g. B. calcium carbonate, zinc oxide. Magnesium oxide, barium hydroxide or strontium hydroxide.

Other successful basic catalysts include the oxides and hydroxides. of cadmium, lead, mercury, manganese, iron, nickel, Cobalts, Cers, Copper and Tin All that is required is that the catalyst is so basic that it forms hydroxyl ions in water or that it is a strong mineral acid, such as hydrochloric or sulfuric acid, able to neutralize.

Based on the weight of the carbamate. should initially be about 2 to 15010 of the basic compound can be applied. However, these amounts are not of crucial importance, as can be seen from the fact that the relationship from catalyst to carbamate necessarily increased as the isocyanate increased is removed from the reaction vessel as the reaction proceeds.

It is best to heat the carbamate and the basic catalyst together to the boil and distilled the reaction products, the 1,8-diisocyanp-menthan, and the alcohol formed from the reaction mixture. It is best to use the to carry out thermal decomposition at reduced pressure.

The following examples serve to illustrate the invention. All parts are parts by weight. Example I 1000 parts of the compound 50 parts of calcium carbonate are placed in a flask equipped with a thermometer, stirrer and an attachment suitable for distillation under reduced pressure. The carbamate and the basic catalyst are heated together to the boil while stirring. First, ethanol is collected in the receiver at 1400 and a pressure of 4 mm Hg. After about 55 minutes the desired reaction product begins to distill over at 1850 and a pressure of 43 mm Hg. When 1880 is reached, the receiver is changed; Within the following 135 minutes, practically the entire reaction product is distilled over at 1900 and a pressure of 36 mm Hg. Petroleum ether was added to the 728 parts of distillate; then the solution obtained is extracted four times with the same volume of water. After the petroleum ether solution has evaporated, a residue of 583 parts remains. After careful fractionation, the fraction boiling at bp.05 = 93 to 96 ° is isolated and identified as 1,8-diisocyan-p-methane. The overall yield of this product is a little over 70%.

Virtually the same results (yields between 60 and 800/0) are obtained when other of the above-mentioned basic compounds in place of calcium carbonate are used, so zinc oxide, sodium acetate, cerium oxide, sodium carbonate. Barium hydroxide, strontium hydroxide and sodium ethylate; in the absence of this basic Compounds, however, no diisocyanate is obtained.

Example II A mixture of 100 parts of 1,8-bis (cyclohexyloxycarhamido) -p-menthane and 10 parts of zinc oxide was in a vacuum of 5 mm with stirring as in the previous example heated. As the reaction proceeded, cyclohexanol was distilled off, the Distillation began when the temperature of the reaction mass reached 1500. The pressure was kept at 40mm. By 1850, the forerun was at a pressure of 40 mm Hg collected, and after changing the template, crude 1,8-diisocyanp-menthan was used Bp 40 = 180 to 205C obtained. The compound was purified by distillation using a 10 cm long column charged with stainless steel coils, cleaned, the yield being approximately 60%.

Example III A mixture of 100 parts of 1,8-bis- (n-octyloxycarbamido) -p-menthane and 8 parts of sodium acetate was done in a similar manner at a print heated by 35 mm Hg. First went a fraction of n-octyl alcohol and finally 1,8-diisocyan-p-menthane, which boiled at bp 25 = 180 to 190 °, over.

After purification as carried out above, the fraction that boiled at bp 1.2 = 100 to 1020, separated off and identified by analysis. It a yield of about 80% was obtained.

Example IV A mixture of 100 parts of 1,8-bis (benzyloxy carbamideo) -p-menthane and 10 parts of ceria was heated to 150 ° at a pressure of 40 mm Hg.

Benzyl alcohol began to pass over at 150 ° (temperature of the reaction mass). When the temperature reached 190 °, the template was changed and raw in it 1,8-diisocyan-p-methane collected.

This was obtained by distillation using a 10 cm long column. which was loaded with stainless steel coils, carefully cleaned. The parliamentary group from bp 0.5 = 94 to 96 ° corresponded in their analytical composition to 1,8-diisocyanp-menthane.

Claims (4)

PATENT CLAIMS: 1. Process for the preparation of 1,8-diisocyanp-menthan of the formula characterized in that a carbamate of the formula in which R 'is any hydrocarbon radical which, however, may be at most benzolically unsaturated, such as a saturated alkyl or cycloalkyl radical or an aralkyl radical, in the presence of a water-soluble metal compound whose 0.1N aqueous solution has a p-value of at least 8 at 250 has, or a water-insoluble metal oxide or hydroxide, which is able to neutralize a strong mineral acid, decomposes thermally and isolates the 1,8-diisocyan-p-methane from the reaction mixture by distillation. 2. The method according to claim 1, characterized in that as Starting compound a carbamate of the above general formula is used in the R 'is an ethyl group. 3. The method according to claim 1 and 2, characterized in that daxk man use calcium carbopnate as a basic catalyst. Publications considered: Ber. German Chem. Ges., Vol. 41. 1908, pp. 4184 to 4185; J. Am. Chem. Soc., Vol. 45, 1923, p. 726: Vol. 48, 1923, P. 99; Beilstein's handb. organ. Chemistry. Vol. III. 4th edition, 1921, main work. P. 32, supplementary work II, 1942, p. 25; Dear. Ann. d. chem., Vol. 562, 1949, pp. 75 to 136.