Patent Description:
Monothiocarbonates are useful starting materials for the synthesis of chemical compounds. So far, however, monothiocarbonates have not been used in any industrial processes in significant amounts.

Different methods for the synthesis of monothiocarbonates are described in the state of the art.

According to the process disclosed in <CIT> alkylene monothiocarbonates are obtained by reacting an epoxide with carbonylsulfide. The availability of carbonylsulfide is limited. Yields and selectivities of alkylene monothiocarbonates obtained are low. <NPL> describe the use of guanidine as catalysts in the process of <CIT>.

A synthesis using phosgene as starting material is known from <CIT>. Phosgene is reacted with hydroxymercaptanes. Yields of monothiocarbonates are still low and by products from polymerization are observed.

Object of <CIT> and <CIT> is a two-step-process for the preparation of ethylene monothiocarbonates. In a first step mercaptoethanol and chloro-carboxylates are reacted to give hydroxyethylthiocarbonate, which is heated in the second step in a presence of metal salt catalyst to the ethylene monothiocarbonate.

According to <CIT> alkylene monothiocarbonates are obtained by reacting mercaptoethanol and a carbonate diester in the presence of a catalytically active salt of thorium.

<NPL> disclose the formation of monothiocarbonate by reacting carbon disulfide and <NUM>,<NUM> dimethyloxirane in the presence of trimethylamine.

<NPL> disclose the formation of monothiocarbonate using epoxide, sulfur and carbon monoxide as reactants in the presence of sodium hydride.

<NPL>) disclose some specific cyclic monothiocarbonates obtained via coupling reaction of carbonyl sulfides with epoxides.

<NPL> also disclose some specific cyclic monothiocarbonates obtained via coupling reaction of carbonyl sulfides with epoxides.

The object of <CIT> are epoxy compositions that comprise compounds with five membered cyclic ring system comprising oxygen and sulfur. The compounds disclosed in <CIT> and in <NPL> cited in <CIT>, are compounds with five membered cyclic ring system comprising at least <NUM> sulfur atoms. Compounds with one sulfur atom are not mentioned.

<CIT> discloses a mold release agent obtained by combining a (meth)acrylic copolymer comprising a five-membered ring dithiocarbonate group-containing (meth)acrylate unit and a higher alkyl (meth)acrylate unit with a cross-linking agent or a curing catalyst.

None of the processes described above has gained industrial importance due to their deficiencies. Many of these processes involve the use of starting materials of low availability, high costs or problematic properties. Furthermore, yields and selectivities, in particular selectivity of structural isomers, obtained are not yet satisfying for production on industrial scale. As a consequence, the availability of thiocarbonates in commercial quantities is low even though thiocarbonates are of high interest as intermediates in chemical synthesis.

Hence, it was an object of this invention to provide a process to produce thiocarbonates which is useful for industrial scale production. The process should not involve expensive starting materials or starting materials of low availability. The process should be easy to perform, should be as economic as possible and give thiocarbonates in high yield and selectivity.

Accordingly, the above process for the preparation of a compound with at least one five-membered cyclic monothiocarbonate group has been found.

A five-membered cyclic monothiocarbonate group is a ring system with <NUM> members, three of them are from the monothiocarbonate -O-C (=O)-S- and the further two members are carbon atoms closing the five-membered cycle.

Starting compound for the process is a compound with at least one epoxy group.

In a preferred embodiment the compound with at least one epoxy group is.

A glycidyl compound is a compound with at least a glycidyl group or a derivative thereof. Examples for i) are epichlorohydrin or derivatives thereof wherein the chloride of epichlorohydrin is replaced by a hydroxy group (glycidol) ether group (glycidyl ether), ester group (glycidyl ester) or amino group (glycidyl amine) or an imide group (glycidyl imide).

Further examples for i) are any compounds obtained by reacting.

In a particularly preferred embodiment, compounds i) are selected from epichlorohydrin, a glycidyl ether, a glycidyl ester, a glycidyl amine or glycidyl imide or a compound with at least one glycidyl group or at least one glycidyl ether group or at least one glycidyl ester group or at least one glycidyl amino group or at least one glycidyl imide group.

The compound may be a compound with only one epoxy group, such epoxy-compounds are usually low molecular weight compounds with a molecular weight below <NUM>/mol, in particular below <NUM>/mol, more specifically below <NUM>/mol. A compound with only one epoxy group could be, for example, epichlorhydrin or a glycidylether or a glycidylester or propylenoxide.

The compound may comprise more than one epoxy group. Such compounds are, for example, fatty acids, fatty acid esters or fatty alcohols with at least two unsaturated groups that have been transferred into epoxy groups. Further compounds with at least two epoxy groups are poly glycidylethers, in particular diglycidyl ethers, for example bisphenol diglycidyl ethers. Compounds which are polymers or oligomers may comprise a high number of epoxy groups. Such compounds are, for example, obtainable by polymerization or copolymerization of monomers with epoxy groups or by converting functional groups of polymers into epoxy groups. Compounds with more than one epoxy group may comprise, for example, up to <NUM>, in particular up to <NUM>, preferably up to <NUM> epoxy groups. Further polymers with epoxy groups are, for example, novolacs that have been epoxidized by reacting them with epichlorhydrin to novolac-polyglycidylether.

Examples for ii) are compounds with one, two or three epoxy groups obtained by oxidizing olefins, di-olefins or tri-olefins, or cyclic olefins, unsaturated fatty acids, fatty acid esters or fatty alcohols.

In a preferred embodiment, the compound with at least one epoxy group is a compound with <NUM> to <NUM>, more preferably <NUM> to <NUM> and in a most preferred embodiment with <NUM> to <NUM>, notably <NUM> or <NUM> epoxy groups.

In the first process step the compound with at least one epoxy group is reacted with phosgene or an alkyl chloroformate thus giving an adduct. Preferably, it is reacted with phosgene. The word phosgene shall include any phosgene substitutes; phosgene substitutes are compounds that set free phosgene. A phosgene substitute is, for example, triphosgene.

Below the reaction of step b) is shown exemplarily for a specific epoxy compound substituted by R and phosgene as reactant.

Two structural isomers of β-chloroalkyl chloroformate A and B are obtained. It is an advantage of the present invention that the product has a high selectivity regarding the structural isomers. In particular, at least <NUM> %, preferably at least <NUM>% usually at least <NUM>% of the adduct correspond to isomer A.

The compound with at least one epoxy group may be reacted with phosgene or an alkyl chloroformate in any stochiometric ratio. Preferably, a very high excess of the compound with at least one epoxy group is avoided, as such a high excess would result in high amounts of unreacted starting compounds which would have to be removed during work-up of the obtained product composition.

Preferably, the phosgene, respectively chloroformate, are used in an amount of <NUM> to <NUM> mol, in particular of <NUM> to <NUM> mol per mol of each epoxy group of the compound with at least one epoxy group. In a particularly preferred embodiment the phosgene, respectively chloroformate, are used in excess.

With at least equimolar amounts of phosgene, respectively chloroformate, epoxy groups that remain unreacted can be avoided. Hence, in a preferred embodiment the phosgene, respectively chloroformate, are used in an amount of <NUM> to <NUM> mol, more preferably of <NUM> to <NUM> mol, in particular <NUM> to <NUM> mol per mol of each epoxy group of the compound with at least one epoxy group.

In case that products are desired that still comprise epoxy groups, a less than equimolar amount of phosgene, respectively chloroformate, is preferably used per mol of each epoxy group. Alternatively, the reaction may be stopped when the desired amount of epoxy groups is still unreacted.

The obtained product may still comprise epoxy groups.

A specific product of interest could be, for example, a compound comprising one epoxy group and one five-membered cyclic monothiocarbonate group. If such a compound is desired, <NUM> mol of phosgene, respectively chloroformate, may, for example, be used per mol of each epoxy group. As an example of a compound comprising one epoxy group and one five-membered cyclic monothiocarbonate group see the reaction scheme below, starting form a di-epoxide and resulting in a compound with one monothiocarbonate and with still one epoxide group.

The phosgene and the chloroformate are preferably a compound of formula II
<CHM>
wherein X is Cl in case of phosgene or a group O-R5 with R5 representing a C1- to C4 alkyl group in case of chloroformate.

In a preferred embodiment the compound with at least one epoxy group is reacted with phosgene.

Preferably, the reaction is performed in presence of a catalyst. Suitable catalysts are salts with a quaternary ammonium cation such as tetraalkylammonium halogenides, in particular chlorides, for example tetrabutylammoniumchloride, tetrahexylammoniumchloride, benzyltributylammonium chloride or trioctylmethylammonium chloride.

Further suitable catalysts are, for example, hexa-alkylguanidinium halogenides, in particular chlorides, quarternary phosphonium halogenides, in particular chlorides, pyridine or other compounds with a ring system comprising nitrogen such as imidazole or alkylated imidazole.

Preferred catalysts are salts with a quaternary ammonium cation, in particular salts of tetra alkyl ammonium, for example tetra (n-butyl) ammonium chloride.

Preferably, the catalyst is used in an amount of <NUM> to <NUM> mol, in particular in an amount of <NUM> to <NUM> mol per mol of epoxy group.

The phosgene or alkyl chloroformate is preferably added to the compound with at least one epoxy group. As the reaction is exothermic, addition of phosgene or alkyl chloroformate is preferably made slowly so that the temperature of the reaction mixture is kept at the desired value. Preferably, the reaction mixture is cooled during the addition.

Preferably, the temperature of the reaction mixture is kept at -<NUM> to <NUM>, notably at <NUM> to <NUM>.

Low molecular compounds with at least one epoxy group are usually liquid; hence, an additional solvent is not required. Preferably, a solvent is used in case of compounds with at least one epoxy group that are solid at <NUM>. Suitable solvents are, in particular aprotic solvents. Suitable solvents are, for example, hydrocarbons, including aromatic hydrocarbons and chlorinated hydrocarbon, such as for example toluene, chloro-benzene or dichloro-benzene.

A preferred solvent for a solid compound with epoxy groups is an additional liquid compound with epoxy groups. The liquid compound together with the solid compound undergo the reaction as described in process steps b) and c). The monothiocarbonate obtained from the liquid compound would usually be liquid as well and, therefore, would serve also as solvent for the most probably solid monothiocarbonate obtained from the solid compound with at least one epoxy group.

When the reaction is completed, unreacted phosgene or chloroformate may be removed from the mixture by distillation. No further work up is necessary. The product mixture obtained comprises a compound with at least one β-chloro alkylchlorformate group. The next process step may follow immediately.

Below the reaction under b) is exemplarily shown for a specific epoxy compound substituted by R and phosgene as reactant. Starting with the β-chloro alkylchlorformates formed above, the second process step c) can be exemplarily shown for Na<NUM>S as reactant as follows:
<CHM>.

In this step the ratio of structural isomers A and B obtained in the first step and hence the selectivity is preserved.

Preferably, the product mixture obtained under b) is used under process step c) without any further work-up.

A solvent may be added in step c). Suitable solvents are, in particular, aprotic solvents. Suitable solvents are, for example, hydrocarbons, including aromatic hydrocarbons and chlorinated hydrocarbon or hydrophilic aprotic solvents, for example ethers such as tetrahydrofuran, dioxane, polyether such as glyms, acetonitrile or dimethylsulfoxid.

The product mixture from step b) is reacted with a compound comprising anionic sulfur.

The compound comprising anionic sulfur is preferably a salt.

The anionic sulfur is preferably S<NUM>-, a polysulfide of formula (Sp)<NUM>- with p being an integral number from <NUM> to <NUM>, preferably from <NUM> to <NUM> or HS<NUM>-.

The cation of the salt may be any organic or inorganic cation. Preferably, it is an inorganic cation, in particular a metal. Usual metal cations are, for example, cations of alkali or earth alkali metals, such as sodium or potassium.

Preferred salts are Na<NUM>S, K<NUM>S, NaSH or KSH or any hydrates thereof.

The salt may be used in combination with a basic compound, in particular a metal hydroxide, such as, in particular, NaOH or KOH. Such an additional basic compound is preferably used in case of salts with SH- as anion.

The anionic sulfur may also be generated in situ, starting from sulfur or a compound comprising sulfur in non-ionic form. For example H<NUM>S may be used as source for anionic sulfur. In presence of a basic compound, for example NaOH (see above), anionic sulfur is obtained from H<NUM>S in situ.

The salt with anionic sulfur, respectively the compound from which anionic sulfur is generated in situ (together referred herein as the sulfur compound), is preferably added to the product mixture obtained in b). The sulfur compound may be added as such or, for example, as solution in a suitable solvent, such as water. In a preferred embodiment, the sulfur compound is dissolved in a solvent, in particular water, and the solution is added.

If the sulfur compound is added as solution in water, a two-phase system comprising an organic and an aqueous phase is obtained and the reaction occurs in such two- phase system. If a one phase system is desired instead, a suitable solvent may be added which acts as intermediary to combine the aqueous and organic phase to one phase again. A suitable solvent may be a hydrophilic aprotic solvent, for example a hydrophilic aprotic solvent listed above.

As the reaction is exothermic as well, addition of the salt, respectively the solution of the salt, is preferably made slowly so that the temperature of the reaction mixture is kept at the desired value. Preferably, the reaction mixture is cooled during the addition.

The reactants may be added or combined in any order. For example, the sulfur compound may be added to the β -chloro alkylchlorformate as described above. Alternatively, the β-chloro alkylchlorformate may be added to the compound comprising anionic sulfur.

Preferably, the temperature of the reaction mixture is kept at -<NUM> to <NUM>° C, notably at -<NUM> to <NUM>° C.

Preferably, the salt is added in an amount of <NUM> to <NUM> mol per mol of each β -chloro alkylchlorformate group of the compound with at least one β -chloro alkylchlorformate group.

In a most preferred embodiment, the salt is added in an amount of <NUM> to <NUM> mol per mol of each β -chloro alkylchlorformate group of the compound with at least one β -chloro alkylchlorformate group, as no significant excess of the salt is required to get a quick and complete reaction of all β -chloro alkylchlorformate groups.

By reaction with the salt the β -chloro alkylchlorformate groups are transferred into five-membered cyclic monothiocarbonate groups. The five-membered ring system is formed from three carbon atoms, one oxygen and one sulfur with a further oxygen double bonded to the carbon atom which is located between the oxygen and the sulfur of the ring system.

If desired, the second process step may be performed in the presence of a catalyst. Such a catalyst is, for example, a phase transfer catalyst such as ammonium salts, heterocyclic ammonium salts and phosphonium salts.

The final product obtained under c) may be worked up by extracting with a hydrophilic solvent, preferably water. In case that the above salt of anionic sulfur has been used in form of an aqueous solution nor further water may be required. The organic and aqueous phase are separated. The organic phase may be washed with water which has preferably a pH of <NUM> to <NUM>, in particular a pH of at least <NUM>. The organic phase comprises the compound with at least one monothiocarbonate group. The aqueous phase comprises unreacted sulfide/hydrogesulfide salt and/or NaCl and at least partially any catalyst added.

Any solvent may be removed from the organic phase by distillation. The obtained compound with at least one monothiocarbonate group may be further purified by distillation or may be used without further purification.

Hence, compounds with at least one five-membered cyclic monothiocarbonate group are obtained by the above process.

A preferred process for the preparation of a compound with one five-membered cyclic monothiocarbonate group comprises.

In case that any of R1a to R4a represent an organic group, such organic group is preferably an organic group with up to <NUM> carbon atoms. In a further preferred embodiment R2a and R4a do not form a five to ten membered carbon ring together with the two carbon atoms of the epoxy group.

In case that any of R1a to R4a represent an organic group, such organic group may comprise other elements than carbon and hydrogen. In particular, it may comprise oxygen, nitrogen, sulfur and chloride. In a preferred embodiment the organic group may comprise oxygen or chloride. R1a to R4a may comprise oxygen for example in form of ether, hydroxy, aldehyde, keto or carboxy groups.

Preferably, at least one of R1a to R4a in formula Ia and accordingly in formulas IIIa and IVa is not hydrogen.

More preferably, two and or three of R1a to R4a in formula Ia and accordingly in formulas Illa and IVa represent hydrogen and the remaining groups R1a to R4a represent an organic group.

Most preferably, three of R1a to R4a in formula Ia and accordingly in formulas Illa and IVa represent hydrogen and the remaining group of R1a to R4a represents an organic group.

In a preferred embodiment R1a or R2a is the remaining group representing an organic group.

The remaining groups or the remaining group of R1a to R4a preferably represent a hydrocarbon group with up to <NUM> carbon atoms which may comprise oxygen, nitrogen or chloride, in particular oxygen.

In a preferred embodiment, the remaining groups or the remaining group represent a group -CH<NUM>-O-R<NUM> or -CH<NUM>-O-C(=O)-R<NUM> or -CH<NUM>-NR<NUM>R<NUM> with R<NUM> to R<NUM> being an organic group with up to <NUM> carbon atoms, preferably up to <NUM> carbon atoms. In particular, R<NUM> to R<NUM> represent an aliphatic, cycloaliphatic or aromatic group, which may comprise oxygen, for example in form of ether groups. In a preferred embodiment, R<NUM> to R<NUM> represent a linear or branched alkyl group, alkoxy group, polyalkoxy group or alkenyl group. In a most preferred embodiment, R<NUM> to R<NUM> represent a linear or branched alkyl group or alkenyl group.

In a most preferred embodiment, the remaining groups or the remaining group represent a group -CH<NUM>-O-R<NUM> or -CH<NUM>-O-C(=O)-R<NUM>.

As preferred compounds with one five-membered cyclic monothiocarbonate group obtained by the process may be mentioned:
<CHM>.

In addition, the monothiocarbonate compounds obtained from epoxides selected from ethylene oxide, propylene oxide, butylene oxide, isobutylene oxide, methyl-<NUM>,<NUM>-epoxycyclohexanecarboxylate, <NUM>,<NUM>-epoxycyclohexylmethyl <NUM>,<NUM>-epoxycyclohexanecarboxylate, are mentioned.

All disclosure in this patent application relating to process steps b) and c) apply to the above preparation of a compound with one five-membered cyclic monothiocarbonate group.

<CHM>
wherein three of R1a to R4a represent hydrogen and the groups R1a to R4a not being hydrogen represent a group CH<NUM>-O-R<NUM> or -CH<NUM>-O-C(=O)-R<NUM> with R<NUM> to R<NUM> being a linear or branched alkyl group, alkoxy group, polyalkoxy group or alkenyl group with at maximum <NUM> carbon atoms have not been produced by processes of the prior art and are now accessible by the process disclosed herein.

Processes for the production of monothiocarbonates known from the prior art usually give mixtures of structural isomers. With the process disclosed herein the content of structural isomers is significantly reduced. Mixtures of isomers A and B with very low amount of B are obtainable, see above.

In a preferred embodiment, the compound of formula IVa is a mixture of two structural isomeric compounds A and B of formula IVa wherein isomer A is a compound with R1a being a group CH<NUM>-O-R<NUM> or CH<NUM>-O-C(=O)-R<NUM> and R2a R3a and R4a being hydrogen and isomer B is a compound with R3a being a group CH<NUM>-O-R<NUM> or CH<NUM>-O-C(=O)-R<NUM> and R1a, R2a and R4a being hydrogen and wherein the mixture consists of <NUM> to <NUM> % by weight of A and <NUM> to <NUM> % by weight of B, based on the sum of A and B. Preferably, the mixture consists of <NUM> to <NUM> %, respectively <NUM> to <NUM> % by weight of A and <NUM> to <NUM> %, respectively <NUM>. <NUM> to <NUM> % by weight of B.

A particularly preferred compound of formula IVa is a compound wherein R2a to R4a in formula IVa represent hydrogen and R1a is a group -CH<NUM>-O-R<NUM> or a group -CH<NUM>-O-C(=O)-R<NUM> with R<NUM> to R<NUM> being an C1 to C14 alkyl group, preferably a C4 to C14 alkyl group.

Disclosed is a very economic and effective process for the production of compounds with at least one five-membered cyclic monothiocarbonate group. The process is suitable for industrial scale production. The process does not involve expensive starting materials or starting materials of low availability. The process gives compounds with at least one five-membered cyclic monothiocarbonate group in high yield and selectivity.

Epoxide was charged to a reactor and kept at -<NUM>° C. The molar amount of epoxide is listed in Table <NUM>. <NUM> mol of tetra(n-butyl ammonium chloride were added per <NUM> mol of epoxide. Thereafter phosgene is added slowly as the reaction is exothermic. When adding the phosgene the temperature was kept via cooling at the temperature listed in the Table. The time of metering phosgene is listed in the Table. The total amount of phosgene was <NUM> mol per <NUM> mol of epoxide. When the addition of phosgene was completed the reaction mixture was further stirred for about (<NUM> hours). Unreacted phosgene was removed by nitrogen stripping. No further work-up was necessary. The obtained β -chloro alkylchlorformates could be used directly in the next step which is the formation of the thiocarbonates.

The epoxide, the obtained β -chloro alkylchlorformates and further details of the reaction are listed in Table <NUM>.

The β -chloro alkylchlorformates are obtained in form of two different structural isomers (stereoisomers) a and b
<CHM>.

The selectivities regarding a and b are listed in the Table <NUM> as well. The total yield listed in Table <NUM> is based on the epoxide used as starting material.

In examples <NUM> and <NUM> the yield and selectivity was determined by <NUM>- und 13C-NMR.

The respective β -chloroalkyl chloroformate from examples <NUM> to <NUM> (<NUM>) and dichloro-methane (<NUM>) are placed in a <NUM> <NUM> neck round bottom flask equipped with a KPG crescent stirrer, dropping funnel, thermometer and a reflux condenser. The solution was cooled down to <NUM>° C with an ice bath before Na<NUM>S (<NUM> equiv. , <NUM> wt% aqueous solution) was slowly added, maintaining the temperature at <NUM> ° C. After the complete addition the ice bath was removed and the reaction mixture allowed to warm to room temperature. After stirring for <NUM> the phases were separated and the aqueous phase was extracted with dichloromethane (<NUM> x <NUM>). The solvent was removed from the combined organic phases under reduced pressure and the residual liquid purified by (Kugelrohr) distillation, yielding the desired cyclic thiocarbonate.

The respective bis-β-chloroalkyl chloroformiate (<NUM>) and dichloromethane (<NUM>) are placed in a <NUM> <NUM> neck round bottom flask equipped with a KPG crescent stirrer, dropping funnel, thermometer and a reflux condenser. The solution was cooled down to <NUM>° C with an ice bath before Na<NUM>S (<NUM> equiv. , <NUM> wt% aqueous solution) was slowly added, maintaining the temperature at <NUM> ° C. After the complete addition the ice bath was removed and the reaction mixture allowed to warm to room temperature. After stirring for <NUM> the phases were separated and the aqueous phase was extracted with dichloromethane (<NUM> x <NUM>). The solvent was removed from the combined organic phases under reduced pressure yielding the desired cyclic monothiocarbonate.

<NUM>-Chloro-<NUM>-butoxy isopropyl chloroformate (<NUM>) is placed in a <NUM> <NUM> neck round bottom flask equipped with a KPG crescent stirrer, dropping funnel, thermometer and a reflux condenser. The liquid was cooled down to <NUM>° C with an ice bath before a solution of NaSH (<NUM> equiv. , <NUM> wt% aqueous solution) containing NaOH (<NUM> equiv. ) was slowly added, maintaining the temperature at <NUM> ° C. After the complete addition, the ice bath was removed and the reaction mixture allowed to warm to room temperature. The reaction was monitored via GC and after <NUM> complete conversion of the chloroformate was observed. The phases were separated and the aqueous phase was extracted with dichloromethane (<NUM> x <NUM>). The solvent was removed from the combined organic phases under reduced pressure yielding the desired cyclic thiocarbonate in ><NUM>% purity.

Glycidylmethacrylate (<NUM> mol) was charged to a reactor and kept at -<NUM>° C. <NUM> mol of tetra(n-butyl ammonium chloride were added. Thereafter phosgene is added slowly as the reaction is exothermic. When adding the phosgene the temperature was kept via cooling at the temperature between <NUM>-<NUM>° C. The total amount of phosgene was <NUM> mol per <NUM> mol of epoxide. When the addition of phosgene was completed the reaction mixture was further stirred for about (<NUM> hours) while raising the temperature to <NUM> ° C. Unreacted phosgene was removed by nitrogen stripping. No further work-up was necessary. The obtained β - chloro alkylchlorformate could be used directly in the next step which is the formation of the monothiocarbonates.

The β -chloroalkyl chloroformiate obtained (<NUM>) was placed in a <NUM> <NUM> neck round bottom flask equipped with a KPG crescent stirrer, dropping funnel, thermometer and a reflux condenser and dichloro-methane (<NUM>) was added. The liquid was cooled down to <NUM>° C with an ice bath before Na<NUM>S (<NUM> equiv. , <NUM> wt% aqueous solution) was slowly added, maintaining the temperature at <NUM> ° C. After the complete addition, the ice bath was removed and the reaction mixture allowed to warm to room temperature. After stirring for <NUM> the phases were separated. GC analysis shows an initial purity of the methacryl-monothiocarbonate of <NUM>%. Recrystallization from methanol results in a methacryl-monothiocarbonate with a purity of ><NUM>%.

Details of the process are listed in Table <NUM>:.

Claim 1:
A compound of formula IVa,
<CHM>
wherein three of R1a to R4a represent hydrogen and the groups R1a to R4a not being hydrogen represent a group CH<NUM>-O-R<NUM> or CH<NUM>-O-C(=O)-R<NUM> with R<NUM> or R<NUM> being a linear or branched alkyl group, alkoxy group, polyalkoxy group or alkenyl group with at maximum <NUM> carbon atoms.