Method for the manufacture of alkoxysilyl-containing thiocarboxylic acid esters

1. A method for the manufacture of an alkoxysilyl-containing thiocarboxylic acid ester of the general formula (I):

R 1 —[C(═O)—S—R 2 —SiR 3 a (OR 4 ) 3-a ] z   (I)

wherein R 1 is a monovalent group selected from straight chain alkyl group containing from 1 to 18 carbon atoms, a branched chain alkyl group containing from 3 to 18 carbon atoms, a cycloalkyl group containing from 5 to 18 carbon atoms, an alkenyl group containing from 2 to 18 carbon atoms, an aryl group containing from 6 to 18 carbon atoms, aralkyl group containing from 7 to 18 carbon atoms or hydrogen, or is a divalent group selected from an alkyl group containing from 1 to 10 carbon atoms, a cycloalkyl group containing from 5 to 10 carbon atoms or phenyl group;

each R 2 is independently a divalent group selected from straight chain alkyl group containing from 1 to 10 carbon atoms, a branched chain alkyl group containing from 3 to 10 carbon atoms, a cycloalkyl group containing from 5 to 10 carbon atoms, an alkenyl group containing from 2 to 10 carbon atoms, an aryl group containing from 6 to 10 carbon atoms or aralkyl group containing from 7 to 10 carbon atoms;

each R 3 is independently a monovalent group selected from straight chain alkyl group containing from 1 to 6 carbon atoms, a branched chain alkyl group containing from 3 to 6 carbon atoms, a cycloalkyl group containing from 5 or 6 carbon atoms, an alkenyl group containing from 2 to 6 carbon atoms, an aryl group containing 6 carbon atoms or an aralkyl group containing from 7 to 10 carbon atoms;

R 4 is independently a monovalent group selected from straight chain alkyl group containing from 1 to 6 carbon atoms, a branched chain alkyl group containing from 3 to 6 carbon atoms, a cycloalkyl group containing from 5 or 6 carbon atoms, an alkenyl group containing from 2 to 6 carbon atoms, an aryl group containing 6 carbon atoms, aralkyl group containing from 7 to 10 carbon atoms, a straight chain alkyl group containing 2 to 6 carbon atoms and a hydroxyl group, an alkyl group containing at least one oxygen atom having the structure —R 2 —(OCH 2 CH 2 ) m (OCH 2 CH(CH 3 )) n OR 1 or a divalent group formed from two R 4 groups being bonded together through a covalent bond, with the provision that (i) if two R 4 groups are bonded together, then a is 0 or 1 and (ii) the sum of m+n is from 1 to 20; and

a, m, n and z are integers wherein a is 0, 1 or 2, m is from 0 to 10, n is from 0 to 10 and z is 1 or 2, and wherein the method comprises:

reacting a thioester of the general formula (II):

R 1 [C(═O)SR 5 ] z   (II)

wherein

each R 5 is independently a monovalent group selected from straight chain alkyl group containing from 1 to 18 carbon atoms, a branched chain alkyl group containing from 3 to 18 carbon atoms, a cycloalkyl group containing from 5 to 18 carbon atoms, an alkenyl group containing from 2 to 18 carbon atoms, an aryl group containing from 6 to 18 carbon atoms, aralkyl group containing from 7 to 18 carbon atoms, and wherein R 1 and z are as defined above,

with a mercapto-functional alkoxysilane of general formula (V):

HS—R 2 —SiR 3 a (OR 4 ) 3-a   (V)

wherein R 2 , R 3 and R 4 and a are as defined above, and/or

an alkali metal salt, an alkaline earth metal salt or a trisubstituted ammonium salt of an alkoxysilyl-functional thiolate of the general formula (III):

M +− S—R 2 —SiR 3 a (OR 4 ) 3-a   (III)

wherein M + is an alkali metal ion, an alkaline earth metal ion or a trisubstituted ammonium ion, and R 2 , R 3 , R 4 and a are as defined above.

2. The method of claim 1 further comprising

(a) contacting the thioester of general formula of (H) with the mercapto-functional alkoxysilane of general formula (V) and/or the alkali metal salt, the alkaline earth metal saltor the trisubstituted ammonium salt of the alkoxysilyl-functional thiolate of general formula (III) prior to the reacting step;

(b) reacting the thioester of general formula (II) with the mercapto-functional alkoxysilane of general formula (V) and/or the alkali metal salt, the alkaline earth metal salt or the trisubstituted ammonium salt of the alkoxysilyl-functional thiolate of general formula (III) of step (a) to further produce a byproduct which is a thiol of general formula (VI):

HSR 5   (VI)

wherein R 5 is as defined above

and/or

a byproduct which is an alkali metal salt, an alkaline earth metal salt or a trisubstituted ammonium salt of a thiolate of general formula (IV):

M +− SR 5   (IV)

wherein M + and R 5 are as defined above which form a mixture comprising the alkoxysilyl-containing thiocarboxylic acid ester of general formula (I), and the byproduct which is the thiol of general formula (VI) and/or the byproduct which is the alkali metal salt, the alkaline earth salt or the trisubstituted ammonium salt of the thiolate of general formula (IV);

(c) removing the byproduct which is the thiol of general formula (VI) and/or the byproduct which is the alkali metal salt, the alkaline earth metal salt or the trisubstituted ammonium salt of the thiolate of general formula (IV) from the mixture formed in step (b) to produce a product mixture containing the alkoxysilyl-containing thiocarboxylic acid ester of general formula (I);

(d) optionally, further treating the product mixture formed in step (c); and

(e) optionally, reacting the byproduct which is the thiol of general formula (VI) and/or the byproduct which is the alkali metal salt, the alkaline earth metal salt or the trisubstituted ammonium salt of the thiolate of general formula (IV) removed from of step (c) with a carboxylic acid to form the thioester of general formula (II), and adding the thioester of general formula (II) to step (a) to prepare the alkoxysilyl-containing thiocarboxylic acid ester of the general formula (I).

3. The method of claim 2 wherein R 1 is a monovalent straight chain alkyl group containing 5 to 11 carbon atoms, a monovalent branched chain alkyl group containing 5 to 11 carbon atoms or a divalent straight chain alkyl group of from 1 to 8 carbon atoms, R 2 is a divalent alkyl group containing 1 to 6 carbon atoms or a branched chain alkyl group containing 3 to 6 carbon atoms, R 3 is methyl, R 4 is monovalent ethyl, 2-hydroxylethyl, 2-hydroxylpropyl, 3-hydoxyl-2-methylpropyl, 2-hydroxylbutyl, 3-hydroxylbutyl or 3-hydroxyl-1,3-dimethylbutyl or where two R 4 are bonded together to form a divalent group R 4 —R 4 — having the structure —CH 2 CH 2 CH 2 —, —CH 2 CH(CH 3 )CH 2 — or —CH 2 CH 2 CH(CH 3 )—, R 5 is a monovalent straight chain alkyl group of from 4 to 8 carbon atoms, a monovalent branched chain alkyl group of from 4 to 8 carbon atoms or a monovalent cycloalkyl group of from 5 to 8 carbon atoms, M + is sodium ion, a is 0 or 1 and z is 1 or 2.

4. The method of claim 2 wherein the alkoxysilyl-containing thiocarboxylic acid ester of general formula (I) is selected from the group consisting of 2-triethoxysilyl-1-ethyl thioacetate; 2-trimethoxysilyl-1-ethyl thioacetate; 2-(methyldimethoxysilyl)-1-ethyl thioacetate; 3-trimethoxysilyl-1-propyl thioacetate; triethoxysilylmethyl thioacetate; trimethoxysilylmethyl thioacetate; triisopropoxysilylmethyl thioacetate; methyldiethoxysilylmethyl thioacetate; methyldimethoxysilylmethyl thioacetate; methyldiisopropoxysilylmethyl thioacetate; dimethylethoxysilylmethyl thioacetate; dimethylmethoxysilylmethyl thioacetate; dimethylisopropoxysilylmethyl thioacetate; 2-triisopropoxysilyl-1-ethyl thioacetate; 2-(methyldiethoxysilyl)-1-ethyl thioacetate; 2-(methyldiisopropoxysilyl)-1-ethyl thioacetate; 2-(dimethylethoxysilyl)-1-ethyl thioacetate; 2-(dimethylmethoxysilyl)-1-ethyl thioacetate; 2-(dimethylisopropoxysilyl)-1-ethyl thioacetate; 3-triethoxysilyl-1-propyl thioacetate; 3-triisopropoxysilyl-1-propyl thioacetate; 3-methyldiethoxysilyl-1-propyl thioacetate; 3-methyldimethoxysilyl-1-propyl thioacetate; 3-methyldiisopropoxysilyl-1-propyl thioacetate; 1-(2-triethoxysilyl-1-ethyl)-4-thioacetylcyclohexane; 1-(2-triethoxysilyl-1-ethyl)-3-thioacetylcyclohexane; 2-triethoxysilyl-5-thioacetylnorbornene; 2-triethoxysilyl-4-thioacetylnorbornene; 2-(2-triethoxysilyl-1-ethyl)-5-thioacetylnorbornene; 2-(2-triethoxysilyl-1-ethyl)-4-thioacetylnorbornene; 6-triethoxysilyl-1-hexyl thioacetate; 1-triethoxysilyl-5-hexyl thioacetate; 8-triethoxysilyl-1-octyl thioacetate; 1-triethoxysilyl-7-octyl thioacetate; 6-triethoxysilyl-1-hexyl thioacetate; 1-triethoxysilyl-5-octyl thioacetate; 8-trimethoxysilyl-1-octyl thioacetate; 1-trimethoxysilyl-7-octyl thioacetate; 10-triethoxysilyl-1-decyl thioacetate; 1-triethoxysilyl-9-decyl thioacetate; 1-triethoxysilyl-2-butyl thioacetate; 1-triethoxysilyl-3-butyl thioacetate; 1-triethoxysilyl-3-methyl-2-butyl thioacetate; 1-triethoxysilyl-3-methyl-3-butyl thioacetate; 3-trimethoxysilyl-1-propyl thiooctanoate; 3-triethoxysilyl-1-propyl thiopalmitate; 3-triethoxysilyl-1-propyl thiooctanoate; 3-triethoxysilyl-1-propyl thiobenzoate; 3-triethoxysilyl-1-propyl thio-2-ethylhexanoate; 3-methyldiacetoxysilyl-1-propyl thioacetate; 3-triacetoxysilyl-1-propyl thioacetate; 2-methyldiacetoxysilyl-1-ethyl thioacetate; 2-triacetoxysilyl-1-ethyl thioacetate; 1-methyldiacetoxysilyl-1-ethyl thioacetate; 1-triacetoxysilyl-1-ethyl thioacetate; bis-(3-triethoxysilyl-1-propyl) dithiophthalate; bis-(3-triethoxysilyl-1-propyl) dithio-iso-phthalate; bis-(3-triethoxysilyl-1-propyl) dithiotere-phthalate; bis-(3-triethoxysilyl-1-propyl) dithiosuccinate, bis-(3-triethoxysilyl-1-propyl) dithiooxalate; bis-(3-triethoxysilyl-1-propyl) dithiosebacate, bis-(3-triethoxysilyl-1-propyl) dithioadipate; thioacetic acid S-(2-methyl-[1,3,2]dioxasilinan-2-ylmethyl) ester; thioacetic acid S-(2-ethoxy-[1,3,2]dioxasilinan-2-ylmethyl) ester; thioacetic acid S-(2,5-dimethyl-[1,3,2]dioxasilinan-2-ylmethyl) ester; thioacetic acid S-(2-ethoxy-5-methyl-[1,3,2]dioxasilinan-2-ylmethyl) ester, thioacetic acid S-[2-(3-hydroxypropoxy)-[1,3,2]dioxasilinan-2-ylmethyl] ester; thioacetic acid S-[2-(3-hydroxy-2-methylpropoxy)-5-methyl-[1,3,2]dioxasilinan-2-ylmethyl] ester; thioacetic acid S-[2-(3-hydroxy-2-methylpropoxy)-5-methyl-[1,3,2]dioxasilinan-2-ylmethyl] ester; thioacetic acid S-[2-(3-hydroxy-3-methylpropoxy)-4-methyl-[1,3,2]dioxasilinan-2-ylmethyl] ester; thioacetic acid S-(2-methyl-[1,3,2]dioxasilinan-2-ylpropyl) ester; thioacetic acid S-(2-ethoxy-[1,3,2]dioxasilinan-2-ylpropyl) ester; thioacetic acid S-(2,5-dimethyl-[1,3,2]dioxasilinan-2-ylpropyl) ester; thioacetic acid S-(2-ethoxy-5-methyl-[1,3,2]dioxasilinan-2-ylpropyl) ester, thioacetic acid S-[2-(3-hydroxypropoxy)-[1,3,2]dioxasilinan-2-ylpropyl] ester; thioacetic acid S-[2-(3-hydroxy-2-methylpropoxy)-5-methyl-[1,3,2]dioxasilinan-2-ylpropyl] ester; thioacetic acid S-[2-(3-hydroxy-2-methylpropoxy)-5-methyl-[1,3,2]dioxasilinan-2-ylpropyl] ester; thioacetic acid S-[2-(3-hydroxy-3-methylpropoxy)-4-methyl-[1,3,2]dioxasilinan-2-ylpropyl] ester; thiopropionic acid S-[2-(3-hydroxy-2-methylpropoxy)-5-methyl-[1,3,2]dioxasilinan-2-ylpropyl] ester; thiopentanoic acid S-[2-(3-hydroxy-2-methylpropoxy)-5-methyl-[1,3,2]dioxasilinan-2-ylpropyl] ester; thiohexanoic acid S-[2-(3-hydroxy-2-methylpropoxy)-5-methyl-[1,3,2]dioxasilinan-2-ylpropyl] ester; 2-ethyl-thiohexanoic acid S-[2-(3-hydroxy-2-methylpropoxy)-5-methyl-[1,3,2]dioxasilinan-2-ylpropyl] ester; thiooctanoic acid S-(2-methyl-[1,3,2]dioxasilinan-2-ylpropyl) ester; thiooctanoic acid S-(2-ethoxy-[1,3,2]dioxasilinan-2-ylpropyl) ester; thiooctanoic acid S-(2,5-dimethyl-[1,3,2]dioxasilinan-2-ylpropyl) ester; thiooctanoic acid S-(2-ethoxy-5-methyl-[1,3,2]dioxasilinan-2-ylpropyl) ester, thiooctanoic acid S-[2-(3-hydroxypropoxy)-[1,3,2]dioxasilinan-2-ylpropyl] ester; thiooctanoic acid S-[2-(3-hydroxy-2-methylpropoxy)-5-methyl-[1,3,2]dioxasilinan-2-ylpropyl] ester; thiooctanoic acid S-[2-(3-hydroxy-2-methylpropoxy)-5-methyl-[1,3,2]dioxasilinan-2-ylpropyl] ester; thiooctanoic acid S-[2-(3-hydroxy-3-methylpropoxy)-4-methyl-[1,3,2]dioxasilinan-2-ylpropyl] ester; thioacetic acid S-(2,4-dimethyl-[1,3,2]dioxasilolan-2-ylmethyl) ester; thioacetic acid S-(2,4-dimethyl-[1,3,2]dioxasilolan-2-ylpropyl) ester; thiooctanoic acid S-(2,4-dimethyl-[1,3,2]dioxasilolan-2-ylpropyl) ester and combinations thereof.

5. The method of claim 2 wherein the thioester of the general formula (II) is selected from the selected from the group consisting of methylthioacetate, ethylthioacetate, allylthioacetate, propylthioacetate, butylthioacetate, pentathioacetate, hexylthioacetate, cyclohexylthioacetate, phenylthioacetate, benzylthioacetate, methylthiooctanoate, ethylthiooctanoate, allylthiooctanoate, propylthiooctanoate, butylthiooctanoate, pentathiooctanoate, hexylthiooctanoate, cyclohexylthiooctanoate, phenylthiooctanoate, benzylthiooctanoate, hexylthioadipate, cyclohexylthioadipate, phenylthioadipate, benzylthioadipate, and combinations thereof.

6. The method of claim 2 wherein the alkali metal salt, the alkaline earth metal salt or the trisubstituted ammonium salt of the alkoxysilyl-functional thiolate of general formula (III) is selected from the group consisting of sodium 3-trimethoxysilylpropanethiolate, sodium 3-triethoxysilylpropanethiolate, sodium 3-diethoxymethylsilylpropanethiolate, sodium trimethoxysilylmethanethiolate, sodium 3-[2-(3-hydroxy-3-methylpropoxy)-4-methyl-[1,3,2]dioxasilinan-2-yl]propanethiolate, sodium 3-[2-(3-hydroxy-2-methylpropoxy)-5-methyl-[1,3,2]dioxasilinan-2-yl]propanethiolate, sodium 3-[2-ethoxy-5-methyl-[1,3,2]dioxasilinan-2-yl]propanethiolate, sodium 3-(2,4-dimethyl-[1,3,2]dioxasilolan-2-yl)propanethiolate, potassium 3-trimethoxysilylpropanethiolate, potassium 3-triethoxysilylpropanethiolate, potassium 3-diethoxymethylsilylpropanethiolate, potassium trimethoxysilylmethanethiolate, potassium 3-[2-(3-hydroxy-3-methylpropoxy)-4-methyl-[1,3,2]dioxasilinan-2-yl]propanethiolate, potassium 3-[2-(3-hydroxy-2-methylpropoxy)-5-methyl-[1,3,2]dioxasilinan-2-yl]propanethiolate, potassium 3-[2-ethoxy-5-methyl-[1,3,2]dioxasilinan-2-yl]propanethiolate, sodium 3-(2,4-dimethyl-[1,3,2]dioxasilolan-2-yl)propanethiolate, trimethylammonium 3-trimethoxysilylpropanethiolate, triethylammonium 3-triethoxysilylpropanethiolate, tri-isopropylammonium 3-diethoxymethylsilylpropanethiolate, trimethylammonium trimethoxysilylmethanethiolate, triethylammonium 3-[2-(3-hydroxy-3-methylpropoxy)-4-methyl-[1,3,2]dioxasilinan-2-yl]propanethiolate, tri-isopropylammonium 3-[2-(3-hydroxy-2-methylpropoxy)-5-methyl-[1,3,2]dioxasilinan-2-yl]propanethiolate, tri-isopropylammonium 3-[2-ethoxy-5-methyl-[1,3,2]dioxasilinan-2-yl]propanethiolate, trimethylammonium 3-(2,4-dimethyl-[1,3,2]dioxasilolan-2-yl)propanethiolate and combinations thereof.

7. The method of claim 2 wherein the mercapto-functional alkoxysilane of general formula (V) is selected from the group consisting of mercapto-functional alkoxysilane can be selected from the group consisting of (3-mercaptopropyl)trimethoxysilane, (3-mercaptopropyl)triethoxysilane, (3-mercaptopropyl)dimethoxymethylsilane, (3-mercaptopropyl)diethoxymethylsilane, (3-mercaptopropyl)dimethyl(methoxy)silane, (3-mercaptopropyl)dimethyl(ethoxy)silane, (2-mercaptoethyl)trimethoxysilane, (2-mercaptoethyl)triethoxysilane, (2-mercaptoethyl)dimethoxymethylsilane, (2-mercaptoethyl)diethoxymethylsilane, (2-mercaptoethyl)dimethyl(methoxy)silane, (2-mercaptoethyl)dimethyl(ethoxy)silane, 2-methyl-[1,3,2]dioxasilinan-2-ylmethyl mercaptan, 2-ethoxy-[1,3,2]dioxasilinan-2-ylmethyl mercaptan, 2,5-dimethyl-[1,3,2]dioxasilinan-2-ylmethyl mercaptan, 2-ethoxy-5-methyl-[1,3,2]dioxasilinan-2-ylmethyl mercaptan, 2-(3-hydroxypropoxy)-[1,3,2]dioxasilinan-2-ylmethyl mercaptan, 2-(3-hydroxy-2-methylpropoxy)-5-methyl-[1,3,2]dioxasilinan-2-ylmethyl mercaptan, 2-(3-hydroxy-2-methylpropoxy)-5-methyl-[1,3,2]dioxasilinan-2-ylmethyl mercaptan, 2-(3-hydroxy-3-methylpropoxy)-4-methyl-[1,3,2]dioxasilinan-2-ylmethyl mercaptan, 2-methyl-[1,3,2]dioxasilinan-2-ylpropyl mercaptan, 2-ethoxy-[1,3,2]dioxasilinan-2-ylpropyl mercaptan, 2,5-dimethyl-[1,3,2]dioxasilinan-2-ylpropyl mercaptan, 2-ethoxy-5-methyl-[1,3,2]dioxasilinan-2-ylpropyl mercaptan, 2-(3-hydroxypropoxy)-[1,3,2]dioxasilinan-2-ylpropyl mercaptan, 2-(3-hydroxy-2-methylpropoxy)-5-methyl-[1,3,2]dioxasilinan-2-ylpropyl mercaptan, 2-(3-hydroxy-2-methylpropoxy)-5-methyl-[1,3,2]dioxasilinan-2-ylpropyl mercaptan, 2-(3-hydroxy-3-methylpropoxy)-4-methyl-[1,3,2]dioxasilinan-2-ylpropyl mercaptan and combinations thereof.

8. The process of claim 2 wherein the byproduct which is the thiol of general formula (VI) has a boiling point that is lower than the boiling point of the mercapto-functional alkoxysilane of general formula (V) and/or the thioester of general formula (II) by less than about 5° C. at an atmospheric pressure of about 1.013 bar.

9. The method of claim 2 further comprising an organic solvent.

10. The method of claim 8 wherein the reaction of the thioester of general formula (II) with the mercapto-functional alkoxysilane of general formula (V) produces the byproduct which is the thiol of general formula (VI).

11. The method of claim 10 , further comprising carrying out the reaction in the presence of a catalyst selected from a Brønsted-Lowry acid or a Lewis acid.

12. The method of claim 10 wherein the byproduct which is the thiol of general formula (VI) is removed by distillation or stripping.

13. The method of claim 10 wherein the mercapto-functional alkoxysilane of general formula (V) is in the amount of from about 0.5 to about 1.5 equivalents based upon the thioester of general formula (II).

14. The method of claim 2 wherein the reaction of the thioester of general formula (II) with the alkali metal salt, the alkaline earth metal salt or the trisubstituted ammonium salt of the alkoxysilyl-functional thiolate of formula (III) produces the byproduct which is the alkali metal salt, the alkaline earth metal salt or the trisubstituted ammonium salt of the thiolate of general formula (IV).

15. The method of claim 14 wherein the reaction of the thioester of general formula (II) with the alkali metal salt, the alkaline earth metal salt or the trisubstituted ammonium salt of the alkoxysilyl-functional thiolate of general formula (III) is carried out at temperatures of from about 15° C. to about 200° C. and at pressures of from about 0.001 bar to about 2 bar.

16. The method of claim 14 wherein the alkali metal salt, the alkaline earth metal salt or the trisubstituted ammonium salt of the alkoxysilyl-functional thiolate of general formula (III) is in the amount of from about 0.5 to about 1.5 equivalents based upon the thioester of general formula (II).

17. The method of claim 2 wherein the step (b) further comprises:

(b1) reacting the byproduct which is the alkali metal salt, the alkaline earth metal salt, or the trisubstituted ammonium salt of the thiolate of formula (IV) with the mercapto-functional alkoxysilane of formula (V) to form the alkali metal salt, the alkaline earth metal salt, or the trisubstituted ammonium salt of the alkoxysilyl-functional thiolate of formula (III) and the byproduct which is the thiol of general formula (VI).

18. The method of claim 17 , wherein the alkoxysilyl-functional thiolate of general formula (V) is used in the amount of from about 0.001 to about 0.9 equivalents based upon the thioester of general formula (II), and the alkali metal salt, the alkaline earth metal salt or the trisubstituted ammonium salt of the alkoxysilyl-functional thiolate of general formula (III) is used in the molar ratio of from about 0.00065 to about 1.5 relative to the mercapto-functional alkoxysilane of general formula (V).

19. The method of claim 17 , wherein the thioester of general formula (II) is reacted with the alkali metal salt, the alkaline earth metal salt or the trisubstituted ammonium salt of the alkoxysilyl-functional thiolate of general formula (III) at temperatures of from about 15° C. to about 200° C. and at pressures of from about 0.001 bar to about 2 bar.

20. The method of claim 17 wherein said method is carried out in a batch process, semi-continuous process or a continuous process.

21. The method of claim 20 , where said continuous process comprises:

(a) continuously contacting the thioester of general formula (H) with the mercapto-functional alkoxysilane of general formula (V) and the alkali metal salt, the alkaline earth metal salt, or the trisubstituted ammonium salt of the alkoxysilyl-functional thiolate of general formula (III) by continuously adding the thioester of general formula (II), the mercapto-functional alkoxysilane of general formula (V) and the alkali metal salt, the alkaline earth metal salt, or the trisubstituted ammonium salt of an alkoxysilyl-functional thiolate of general formula (III) into a first reaction vessel;

(b) continuously reacting the thioester of general formula (H) with the alkali metal salt, the alkaline earth metal salt or the trisubstituted ammonium salt of the alkoxysilyl-functional thiolate of general formula (III) of step (a) in the first reaction vessel to produce the alkoxysilyl-containing thiocarboxylic acid ester of general formula (I) and the byproduct alkali metal salt, alkaline earth metal salt or trisubstituted ammonium salt of the thiolate of general formula (IV);

(b1) continuously reacting the alkali metal salt, the alkaline earth metal salt or the trisubstituted ammonium salt of thiolate of general formula (IV) formed in step (b) with the mercapto-functional alkoxysilane of general formula (V) to form the alkali metal salt, the alkaline earth metal salt, or the trisubstituted ammonium salt of the alkoxysilyl-functional thiolate of general formula (III) and the byproduct thiol of the general formula (VI) in the first reaction vessel, wherein the reactions of step (b) and (b1) form a reaction mixture containing the alkoxysilyl-containing the thiocarboxylic acid ester of general formula (I), the thioester of general formula (II), the alkali metal salt, the alkaline earth metal salt, or the trisubstituted ammonium salt of the alkoxysilyl-functional thiolate of general formula (III) and the mercapto-functional alkoxysilane of general formula (V), and the alkali metal salt, the alkaline earth metal salt, and/or the trisubstituted ammonium salt of thiolate of general formula (III) and the byproduct thiol of general formula (VI);

(c) continuously removing the reaction mixture of step (b1) from the first reaction vessel and transferring the reaction mixture to a distillation apparatus;

(c1) continuously separating the byproduct thiol of general formula (VI) from the other components in the reaction mixture of step (b1) by passing the reaction mixture through distillation apparatus, forming a separated byproduct thiol of general formula (VI) and a mixture of other components;

(c2) continuously removing a portion of the other component of step (c1)

(c3) continuously recycling the remaining portion of other component of step (c1) to the first reaction vessel;

(d) continuous transferring the mixture of other component of step (c2) to a second reactor for further treatment to form the alkoxysilyl-containing thiocarboxylic acid ester of general formula (I);

(d1) continuous transferring the alkoxysilyl-containing thiocarboxylic acid ester of general formula (I) of step (d) to a storage vessel;

(e) optionally, using the separated byproduct thiol of general formula (VI) of step (c1) with a carboxylic acid to prepare the thioester of general formula (II), and transferring the thioester of general formula (II) to the first reaction vessel of step (a) to step (a) to prepare the alkoxysilyl-containing thiocarboxylic acid ester of the general formula (I).

22. The method of claim 2 , wherein the thioester of general formula (II) is prepared by reaction of a carboxylic acid of general formula (VII):

R 1 (COOH) z   (VII)

wherein R 1 and z are as defined herein, in the presence of at least one compound selected from the group consisting of an acid catalyst, a dehydrating agent and moisture scavenger.

23. An alkoxysilyl-containing thiocarboxylic acid ester composition comprising:

(i) an alkoxysilyl-containing thiocarboxylic acid ester of the general formula (I):

R 1 —[C(═O)—S—R 2 —SiR 3 a (OR 4 ) 3-a ] z   (I)

where R 1 is a monovalent group selected from straight chain alkyl group containing from 1 to 18 carbon atoms, a branched chain alkyl group containing from 3 to 18 carbon atoms, a cycloalkyl containing from 5 to 18 carbon atoms, an alkenyl containing from 2 to 18 carbon atoms, an aryl containing from 6 to 18 carbon atoms, aralkyl containing from 7 to 18 carbon atoms or hydrogen, or is a divalent group selected from an alkyl containing from 1 to 10 carbon atoms, a cycloalkyl containing from 5 to 10 carbon atoms or phenyl;

each R 2 is independently a divalent group selected from straight chain alkyl group containing from 1 to 10 carbon atoms, a branched chain alkyl group containing from 3 to 10 carbon atoms, a cycloalkyl group containing from 5 to 10 carbon atoms, an alkenyl group containing from 2 to 10 carbon atoms, an aryl group containing from 6 to 10 carbon atoms or aralkyl group containing from 7 to 10 carbon atoms;

each R 3 is independently a monovalent group selected from straight chain alkyl group containing from 1 to 6 carbon atoms, a branched chain alkyl group containing from 3 to 6 carbon atoms, a cycloalkyl group containing from 5 or 6 carbon atoms, an alkenyl group containing from 2 to 6 carbon atoms, an aryl group containing 6 carbon atoms or an aralkyl group containing from 7 to 10 carbon atoms;

R 4 is independently a monovalent group selected from straight chain alkyl group containing from 1 to 6 carbon atoms, a branched chain alkyl group containing from 3 to 6 carbon atoms, a cycloalkyl group containing from 5 or 6 carbon atoms, an alkenyl group containing from 2 to 6 carbon atoms, an aryl group containing 6 carbon atoms, aralkyl group containing from 7 to 10 carbon atoms, a straight chain alkyl group containing 2 to 6 carbon atoms and a hydroxyl group, an alkyl group containing at least one oxygen atom having the structure —R 2 —(OCH 2 CH 2 ) m (OCH 2 CH(CH 3 )) n OR 1 or a divalent group formed from two R 4 groups being bonded together through a covalent bond, with the provision that (i) if two R 4 groups are bonded together, then a is 0 or 1 and (ii) the sum of m+n is from 1 to 20;

a, m, n and z are integers wherein a is 0, 1 or 2, m is from 0 to 10, n is from 0 to 10 and z is 1 or 2, and

(ii) a thioester of the general formula (II):

R 1 [C(═O)SR 5 ] z   (II)

 wherein

R 1 is a monovalent group selected from straight chain alkyl group containing from 1 to 18 carbon atoms, a branched chain alkyl group containing from 3 to 18 carbon atoms, a cycloalkyl containing from 5 to 18 carbon atoms, an alkenyl containing from 2 to 18 carbon atoms, an aryl containing from 6 to 18 carbon atoms, aralkyl containing from 7 to 18 carbon atoms or hydrogen, or is a divalent group selected from an alkyl containing from 1 to 10 carbon atoms, a cycloalkyl containing from 5 to 10 carbon atoms or phenyl;

each R 5 is independently a monovalent group selected from straight chain alkyl group containing from 1 to 18 carbon atoms, a branched chain alkyl group containing from 3 to 18 carbon atoms, a cycloalkyl group containing from 5 to 18 carbon atoms, an alkenyl group containing from 2 to 18 carbon atoms, an aryl group containing from 6 to 18 carbon atoms, aralkyl group containing from 7 to 18 carbon atoms, and wherein R 1 and z is an integer wherein z is 1 or 2.

24. The alkoxysilyl-containing thiocarboxylic acid ester composition of claim 23 wherein the composition contains from about 70 to about 99.9 weight percent alkoxysilyl-containing thiocarboxylic acid ester of formula (I) and from 0.1 to about 30 weight percent thioester of formula (II), based on the total weight of the alkoxysilyl-containing thiocarboxylic acid of formula (I) and thioester of formula (II).

25. The alkoxysilyl-containing thiocarboxylic acid ester composition of claim 23 further comprising a mercapto-functional alkoxysilane of general formula (V):

HS—R 2 —SiR 3 a (OR 4 ) 3-a   (V)

wherein R 2 , R 3 , R 4 and a are defined above.

26. The alkoxysilyl-containing thiocarboxylic acid ester composition of claim 25 wherein the mercapto-functional alkoxysilane of general formula (V) is from 0.1 to 50 weight percent, based on the total weight of the alkoxysilyl-containing thiocarboxylic acid (i) and thioester (ii).

27. A rubber composition comprising the alkoxysilyl-containing thiocarboxylic acid ester composition of claim 23 .

28. The rubber composition of claim 27 further comprising a mercapto-functional alkoxysilane of formula (V).