FR2521990A2 - Mercaptan prodn. from olefinic cpd. and hydrogen sulphide - using xanthene deriv. as photoinitiator catalyst - Google Patents

Abstract

Mercaptans are synthesised by the photochemical reaction of an olefinic cpd. with H2S in the presence of an initiator of formula (I). (Y is O or S; X is O, S , Se, -CH2, -CH2CH2-, SO2, CO, CS, NR' (R' is a hydrocarbon gp.), -P(R)-, P(OR)-, -P(OR)3- or -P(R)3-(R is alkyl, aryl, H or halogen) and R1-R8 are H, halogen, alkoxy, alkyl and/or aryl). Process gives improved yield of mercaptans and can be effected either with or without an organic solvent such as an organic sulphide, a hydrocarbon or an ether. When using an organic sulphide, the advantage is enhanced in that the latter may be that which is obtd. as by-prod. of the reaction itself.

Description

 The invention relates to an improved process for the preparation of mercaptans from olefinic compounds which are reacted with hydrogen sulfide. It relates in particular to new initiators making it possible to carry out this reaction under the effect of ultraviolet radiation.

où Y est 0 ou S, tandis que X désigne un élément 0, S ou
Se, ou bien un groupe S02, oe, CS, NR', R' étant un radical hydrocarboné, ou encore un groupement au phosphore tri- ou pentavalent, notamment

où R peut désigner un alkyle, un aryle, un H ou un halogènes
Les symboles R à R8 désignent des atomes ou groupes semblables ou différents, tels que H, halogène, alcoxy ou/et alkyle.A process of this type is described in main patent application No. 81 04956 of March 12, 1981; a new group of initiators has been defined therein constituted by xanthene derivatives which can be represented by the formula

where Y is 0 or S, while X denotes an element 0, S or
Se, or else a group SO2, oe, CS, NR ', R' being a hydrocarbon radical, or else a group with tri- or pentavalent phosphorus, in particular

where R can denote an alkyl, an aryl, an H or a halogen
The symbols R to R8 denote similar or different atoms or groups, such as H, halogen, alkoxy and / or alkyl.

 Initiators of this new type have made it possible to obtain a more advanced conversion of the treated olefin and an hourly production of mercaptan greater than with the initiators of the prior art, in particular ethoxyphenylacetophenone, or even that with the benzophenone-tributylphosphite system which gives excellent results.

 The present invention is based on the fact that the advantages of the xanthene initiators, described above, are found when X is a hydrocarbon group -CH2- or -CH2CH2-, and that the corresponding compounds have interesting physical properties, facilitating their use . This is how we have more soluble or liquid initiators, the implementation of which is easier.

 According to the invention, the median cycle can be 6 or 7 elements, the latter configuration corresponding to the presence of -2CH2- in X; if Y is an oxygen, the compound, which in this case is dibenzo-suberone, is in the liquid state, easily manipulated, moreover easily accessible industrially. The same is true of thlo-dibenzo-suberone, in which Y is a sulfur atom, X being -CH2CH2-.

 The other important initiators according to the invention are the anthron, in which X is -CH2- and Y an atom of O, the thioanthrone also having -oe2- in X, but an atom of S in Y. Substituted derivatives , where one or more of the symbols R1 to R8 may be halogens, alkyls, alkoxy or aryls, are also suitable for carrying out the invention.

 A particular advantage of the initiators according to the invention lies in that they can optionally be used under atmospheric pressure; although, under these conditions, the conversion rate of the olefin and the hourly production of mercaptan are lower than under a pressure of several bars, they are clearly stronger than with the old initiators, such as organic phosphites alone or acetophenones used under the same conditions. The absence of secondary products, other than the corresponding sulphide, makes it possible to easily separate the mercaptan formed and to recycle the olefin and the hydrogen sulphide.

 The invention is illustrated by the nonlimiting examples which follow.

EXAMPLE 1
In the apparatus and according to the procedure described in Example 1 (page 6, lines 4-15) of the main patent application No. 81 04956, dodecylmercaptan is prepared with, as initiators, dibenzo-suberone (X being -CH2CH2- and Y oxygen) and thio-dibenzosubone (same X, atom S in Y).

The following results are obtained.

Initiators Conversion% Production of and their flows of dodecene dodecylmeren moles / hour captan, g / h
Dibenzosuberone 1.7 x 10-4 + tributyl phosphite ... 78% 258
5 x 10-3
Dibenzosuberone 1.7 x 10-4 + phosphite of "... 79% 260
tridecyle 6 x 10-
Dibenzosuberone 1.7 x 10 + tributylphos- ... 88% 274
phine 3.5 x 10
Thiodibenzosuberone 10
1.7 x + tributylphos- ... 87% 272
phine 3.5 x 10 α -ethoxy α; - phenyl acetophenone 2 x 10- ...... 65% 222 (initiator according to US patent 4,140,604 zon sees that the dibenzosuberones, just like the xanthene derivatives of the patent main, used in much lower doses than the initiators of the known technique, give better results than the latter.

EXAMPLE 2
The pyrex photochemical reactor is of the conventional plunging lamp type, coaxial; its glass inlet is sintered at the base to ensure good diffusion of hydrogen sulfide and propylene gases. The irradiated volume is 90 ml. This reactor, thermostatically controlled by an external double jacket, operates discontinuously at ambient pressure, the gas flow rates being kept constant during the experiment. They are in particular 30 l / hour for H2S and 30 l / h for propylene. The solvent is diethylene glycol dimethyl ether and the temperature at which it is saturated with hydrogen sulfide and propylene is 10 C. The concentration of photosensitizer corresponds to the optimum of the intensity absorbed in the reactor. The light source is a low pressure mercury re-emission lamp centered on 350 nm. Its power is 8 W. After 30 minutes, the quantities of mercaptan formed and the% of propylene transformed were those of the table below.

Initiator Production% of and its concentration of propyl- Propylene in moles / liter mercaptan converted
g
Dibenzosuberone 0.03 + tributyl phosphite 0.06 .. 4.38 20.8%
Dibenzosuberone 0.03 + tridecyl phosphite 0.06 21.1% Dibenzosubone 0.03 # .. 5.20 23% + tributylphosphine 0.04
Thiodibenzosuberone o, oes + trioctyl phosphite 0.06 .. 4.46 21.3%
Thiodibenzosubone 0.035 + tributylphosphine 0.04 .. 5.31 22.8% a-ethoxy a-phenyl
acetophenone 0.09 ............. 3.32 19%
Tributyl phosphite only 0.09 .1.65 8.6%
These results show that the initiators according to the invention have advantages, even if the reaction is carried out at atmospheric pressure, without excess of H2S with respect to the olefin.

Although the examples relate to initiator systems comprising organic phosphorus compounds, it is understood that these can be replaced or accompanied by other compounds of elements of the group
VA of the Periodic Table, in particular derivatives of bismuth, arsenic or antimony.

 As for the olefinic compounds capable of being used in the process, they are indicated in the main patent; they can, in particular, carry substituents such as halogens, alcohols, carboxyl, alkoxy, acids, esters, for example alkyl or / and aryl maleates or fumarates.

 The organic sulphide, byproduct of the reaction of H2S with the olefin, can advantageously serve as a solvent for the reaction medium. Other solvents are indicated in the main patent application.

Claims (8)

Claims  1. Process for the synthesis of mercaptans for the photochemical reaction of an olefinic compound with hydrogen sulfide. in the presence of an initiator made up of a posed comxanthene / of structure t

 where Y is 0 or S, the symbols R1 to R8 denote atoms or groups which are similar or different, in particular / Walogens, alkoxy, alkyls and / or aryls, characterized in that X is a CH2 or -CH2CH2- group.  2. Method according to claim 1, in which an organic compound of an element from group VA of the Classification of Elements is added to the reaction medium, characterized in that this compound is accompanied by a xanthene derivative in which the group X is - CH2- or -CH2CH2-.  3. Method according to claim 1 or 2, wherein the reaction medium contains, per liter, 0.001 to 0.1 mole of each of the initiators.  4. Method according to one of the preceding claims, in which the treated olefin (s) may contain halogen, alcohol, carboxyl, alkoxy, acids, esters, maleates, alkyl and / or aryl fumarates.  5. Method according to one of claims 2 to 4, wherein the organic compound of the elements of group V A is a phosphite or an alkyl or aryl phosphine.  6. Method according to one of claims 2 to 4, wherein the element of group V A is bismuth, arsenic or antimony.  7. Method according to one of the preceding claims, in which the reaction medium contains a solvent, characterized in that this is an organic sulphide, in particular that which is formed incidentally in the reaction itself.  8. Method according to one of the preceding claims, characterized in that the initiator used consists of one or more of the compounds: xanthone, xanthione, thioxanthone, dibenzosuberone or / and thio-dibenzosuberone.