Process for preparing ionones

Details Process for preparing ionones Process for preparing ionones

1998-11-13

2000-10-31

Padmanabhan, Sreeni

Organic compounds -- part of the class 532-570 series

Organic compounds

Oxygen containing

568349, C07C 4921

Patent

active

061405426

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention relates to an improved process for the continuous preparation of .alpha.- and/or .beta.-ionone or homologs of these compounds by cyclizing pseudoionones using concentrated sulfuric acid in the presence of organic solvents or diluents and by diluting the reaction mixture with water.
2. Description of the Background
It is known that a mixture of .alpha.- and .beta.-ionones is obtained on cyclization of pseudoionone in the presence of acids such as sulfuric acid or phosphoric acid. The ratio of the amounts in which these compounds are produced depends greatly on the conditions under which the reaction takes place.
Since both .alpha.-ionone and .beta.-ionone are of great industrial importance, there has been no lack of attempts to develop a maximally advantageous process for their preparation.
Processes for cyclizing pseudoionone with concentrated sulfuric acid have proven particularly suitable. Since this reaction is highly exothermic, it is very important to remove the heat produced in the reaction as quickly as possible in order to avoid local overheating. For this purpose, in the known processes, diluents have been added to the reaction mixture. Thus, for example, DE Patents 10 80 105 and 16 68 505 disclose the use of aliphatic or cycloaliphatic hydrocarbons. The disadvantage of this process is that resins are relatively quickly deposited in the reaction vessels in the procedure described therein, and interfere with continuous operation.
According to IN patent 77 225, the reaction is carried out in the presence of aliphatic chlorinated hydrocarbons such as methylene chloride, ethylene dichloride, chloroform and tetrachloromethane at temperatures from -10.degree. C. to +10.degree. C.
According to the description in DE-A 15 68 108, this Indian process is disadvantageous because the aliphatic chlorinated hydrocarbons eliminate hydrogen chloride with sulfuric acid, leading within a short time to corrosion of the apparatus used. To avoid these disadvantages, it is recommended to carry out the cyclization at -25.degree. C. to +10.degree. C. in a mixture of low-boiling hydrocarbons and chlorinated hydrocarbons. The disadvantage of the two last-mentioned processes is that the reaction temperature must be kept low with costly coolants in order to obtain good ionone yields.
Further known processes entail removing the considerable heat of cyclization by evaporative cooling with liquid gases. Thus, liquid sulfur dioxide [sic] is used in the process of DE patent 16 68 496, propane, butane or isobutane is used in the process of DE patent 16 68 505, and methyl chloride is used in the process of DE patent 19 17 132, at temperatures from -25.degree. C. to room temperature, preferably temperatures below +10.degree. C.
The results obtained in these processes are generally quite good. The disadvantage thereof is the large expenditure necessary for reliquefying the gas vaporized in the reaction.
Further processes for preparing .beta.-ionone are disclosed in CS patent 179 046, SU patent 458 540 and SU patent 547 445, wherein thorough mixing of the reactants and rapid removal of heat are achieved by using a thin film reactor. The disadvantage of the two last-mentioned processes is that only about 3 to 6 kg of .beta.-ionone are obtained per m.sup.2 of thin film area and hour, and thus transfer to the industrial scale would result in enormous apparatus. The disadvantage of the process in the Czech patent is that temperatures between 10 and 15.degree. C. must be used to obtain good yields, which makes costly coolants necessary once again.
In all the known processes there is always formation of a mixture of .alpha.- and .beta.-ionones. According to DE patents 10 80 105, 16 68 496 and 16 68 505, .beta.-ionone is preferentially obtained at reaction temperatures from -20 to 0.degree. C., while the .alpha.-ionone content increases at temperatures from -10 to 25.degree. C.
In addition, EP 133 668 discloses a process for the continuous preparation of ionones, in which th

REFERENCES:
patent: 4565894 (1986-01-01), Hertel et al.
Chemical Abstracts, vol. 081, #07, abstract # 037679b, Aug. 19, 1974.
Chemical Abstracts, vol. 083, #01, abstract #010527e, Jul. 7, 1975.

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