Process for the dehydrochlorination of chlorinated hydrocarbons

Abstract

A process for the dehydrochlorination of a chlorinated hydrocarbon comprising at least one chlorine atom and at least one hydrogen atom on vicinal carbon atoms to yield the corresponding unsaturated hydrocarbon, said process comprising contacting the chlorinated hydrocarbon with a guanidinium salt or its guanidine precursor.

Claims

1. A process for the dehydrochlorination of a chlorinated hydrocarbon comprising at least one chlorine atom and at least one hydrogen atom on vicinal carbon atoms to yield the corresponding unsaturated hydrocarbon, said process comprising contacting the chlorinated hydrocarbon with a guanidinium salt or its guanidine precursor wherein the guanidine precursor is selected from the group of compounds of formula (I): ##STR00004## wherein each of R, R.sup.1, R.sup.2, R.sup.3 and R.sup.4 is independently selected from the group consisting of H and C.sub.1-C.sub.12 linear or branched alkyl, optionally substituted; or wherein R, R.sup.1, R.sup.2 and R.sup.3 may be comprised in an aliphatic or aromatic cyclic structure, optionally containing heteroatoms; or wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 may be a monocyclic or polycyclic aromatic radical optionally containing heteroatoms and/or optionally substituted.

2. The process according to claim 1 wherein the guanidinium salt forms a coordination product with HCl produced in the dehydrochlorination reaction.

3. The process according to claim 2 further comprising the steps of: heating the coordination product of the guanidinium salt with HCl to a temperature suitable to release HCl; and separating HCl from the guanidinium salt.

4. The process according to claim 2, wherein the process is carried out at a temperature equal to or higher than the temperature suitable to release HCl from the coordination product of the guanidinium salt with HCl.

5. The process according to claim 2, wherein the process is carried out at a temperature lower than the temperature suitable to release HCl from the coordination product of the guanidinium salt with HCl and wherein the process further comprises the steps of separating said coordination product before performing the step of heating to a temperature suitable to release HCl; and separating HCl from the guanidinium salt.

6. The process according to claim 5 further comprising the step of reusing the guanidinium salt into the dehydrochlorination step of the process.

7. The process according to claim 1, wherein the chlorinated hydrocarbon is selected from the compounds of formula (II): R.sub.hR.sub.h1CCl—CHR.sub.h2R.sub.h3 wherein each of R.sub.h, R.sub.h1, R.sub.h2 and R.sub.h3 is independently selected from the group consisting of H, Cl, and C.sub.1-C.sub.10 optionally fluorinated alkyl.

8. The process according to claim 7 wherein R.sub.h1═R.sub.h3═H and R.sub.h═R.sub.h2═Cl and the corresponding unsaturated hydrocarbon is vinylidene chloride.

9. The process according to claim 1, wherein R is H and each of R.sup.1, R.sup.2, R.sup.3 and R.sup.4 is independently selected from the group consisting of H, C.sub.1-C.sub.12 linear or branched, optionally substituted alkyl, and monocyclic or polycyclic aromatic radical optionally substituted and/or optionally containing heteroatoms.

10. The process according to claim 1, wherein R.sup.1═R.sup.2═R.sup.3═R.sup.4═CH.sub.3.

11. The process according to claim 1, wherein the guanidine precursor of formula (I) is selected from the consisting of compounds of formulae (G-1) and (G-2): ##STR00005## wherein R.sub.N in formula (G-2) is H or a C.sub.1-C.sub.12 linear or branched, optionally substituted, alkyl.

12. The process according to claim 1, wherein the process is carried out in liquid phase in the presence of a solvent.

13. The process according to claim 12 wherein the solvent is selected from the group consisting of ketones, sulphoxides, sulfones, amides, pyrrolidones, ethers, and ionic liquids.

14. The process according to claim 3, wherein the process is carried out at a temperature equal to or higher than the temperature suitable to release HCl from the coordination product of the guanidinium salt with HCl.

15. The process according to claim 3, wherein the process is carried out at a temperature lower than the temperature suitable to release HCl from the coordination product of the guanidinium salt with HCl and wherein the process further comprises the steps of separating said coordination product before performing the step of heating to a temperature suitable to release HCl; and separating HCl from the guanidinium salt.

16. The process according to claim 15 further comprising the step of reusing the guanidinium salt into the dehydrochlorination step of the process.

Description

EXAMPLES

General Procedure for the Dehydrochlorination of 1,1,2-trichloroetane to Vinylidene Chloride

(1) The guanidinium salt (or the guanidine precursor) and the solvent (50 mL) were placed in a 100 mL glass, 4-necked round-bottomed flask reactor equipped with a magnetic stirrer, a condenser, a thermometer, a digital N.sub.2 flow control apparatus and a syringe pump equipped with a polypropylene or glass syringe and a PTFE feeding line and needle. The apparatus further comprised a graduated Pyrex test tube immersed in a Dewar containing a dry-ice/acetone slurry (T=−78° C.) connected to the reactor condenser head by means of a PTFE feeding line for the recovery of the gaseous reaction products.

(2) The reactor was purged with N.sub.2 for 30 minutes at 20° C., the condenser is cooled to −10° C. and the N.sub.2 flow set at a rate of 0.6 N-L/h. The stirring rate was set at 1000 rpm. 1,1,2-trichloroethylene was added to the heterogeneous reaction mixture at a fixed rate of 0.2 mL/h (2.154 mmoles/h) with the syringe pump. The glass reactor was dipped in an oil bath and heated to a temperature equal to or greater than the HCl release temperature determined for the guanidine precursor with a stirring rate of 1000 rpm. Total reaction time was recorded with regular intermediate samplings. At the end of each reaction period, the reaction products were analyzed and identified by quantitative .sup.1H-NMR, GC and GC-MS analysis.

(3) The results were analyzed in order to determine: rate constant of the 1.sup.st order catalytic reaction (k.sub.C; dehydrochlorination promoted by guanidinium salt); total conversion of 1,1,2-trichloroethane (C.sub.112TCE); selectivity in vinylidene chloride formation in the catalytic process (S.sub.VDC). All results are summarized in Table 1.

Examples 1-3: Dehydrochlorination with Tetramethylguanidinium Hydrochloride (TMGNH2(+)Cl(−))

(4) Following the General Procedure, dehydrochlorination of 1,1,2-trichloroethylene was carried out in the presence of tetramethylguanidinium chloride in three different solvents: tetraglyme, dimethylsulfoxide (DMSO) and 1-butyl-3-methyl imidazolium chloride under the following experimental conditions:

(5) Ex. 1: tetraglyme; TMGNH.sub.2.sup.(+)Cl.sup.(−): 12.45 mmoles; reaction temperature: 177° C.; reaction time: 48.5 h.

(6) Ex. 2: DMSO (120 mL); TMGNH.sub.2.sup.(+)Cl.sup.(−): 36 mmoles; reaction temperature: 150° C.; reaction time: 7.5 h.

(7) Ex. 3: 1-butyl-3-methyl imidazolium chloride ([C.sub.4mim]Cl) (124 mL); TMGNH.sub.2.sup.(+)Cl.sup.(−): 36 mmoles; reaction temperature: 177° C.; reaction time: 18 h.

(8) The 1.sup.st order catalytic reaction rate constants, selectivities in vinylidene chloride and conversions of 1,1,2-trichloroethylene are reported in Table 1.

Example 4: Dehydrochlorination with 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) in Tetraglyme

(9) Following the General Procedure, dehydrochlorination of 1,1,2-trichloroethylene was carried out in the presence of 1,5,7-triazabicyclo[4.4.0]dec-5-ene (12.45 mmoles) as the guanidine precursor in tetraglyme as the solvent. The reaction temperature was set at 170° C. and the reaction was monitored for 30 h. The reaction rate constants, selectivity in vinylidene chloride and conversion of 1,1,2-trichloroethylene are reported in Table 1.

Example 5: Dehydrochlorination with 1,5,7-triazabicyclo[4.4.0]dec-5-ene Supported on SiO2 in Tetraglyme

(10) Supported 1,5,7-triazabicyclo[4.4.0]dec-5-ene was prepared according to a modification of the procedure disclosed in CAUVEL, A., et al. Monoglyceride synthesis by heterogeneous catalysis using MCM-41 type silicas functionalized with amino groups. J. Org. Chem. 1997, vol. 62, p. 749-751.

(11) The dehydrochlorination process was carried out following the General Procedure employing the supported guanidine precursor (12.45 g, 12.45 mmoles, 1 mmol TBD/1 g silanized support) in tetraglyme (50 mL) at 182° C. for 30 h total reaction time. The results are reported in Table 1.

Comparative Example 1 and 2: Dehydrochlorination with Triethylamine (TEA) or 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) in Tetraglyme

(12) Following the General Procedure, dehydrochlorination of 1,1,2-trichloroethylene was carried out replacing the guanidine precursor with triethylamine (CE1: 12.45 mmol; reaction temperature 130-135° C.; reaction time: 30 h) or with 1,8-diazabicyclo[5.4.0]undec-7-ene (CE2: 12.45 mmoles; reaction temperature 190° C.; reaction time: 30 h). Results are reported in Table 1.

(13) TABLE-US-00001 TABLE 1 Precursor/ k.sub.C C.sub.112TCE S.sub.VDC Example solvent (min.sup.−1) (mol %) (mol %) Ex.1 TMGNH.sub.2.sup.(+)Cl.sup.(−)/ 0.0121 78 62 tetraglyme Ex.2 TMGNH.sub.2.sup.(+)Cl.sup.(−)/ 0.1 95 85 DMSO Ex. 3 TMGNH.sub.2.sup.(+)Cl.sup.(−)/ 55 48 ([C.sub.4mim]Cl Ex. 4 TBD/tetraglyme 0.012 83 60 Ex. 5 supported TBD/ 0.095 60 61 tetraglyme CEx. 1 TEA/tetraglyme 0.0 28* 96* CEx. 2 DBU/tetraglyme 0.0059 78 55 *Selectivity and conversion obtained with non-catalytic process

(14) When the dehydrochlorination process is carried out in the presence of triethylamine conversion of 1,1,2-trichoroethane to vinylidene chloride takes place stoichiometrically. Once all the triethylamine has reacted, forming the triethyl ammonium chloride salt, the process stops.

(15) The dehydrochlorination process proceeds catalytically in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene. However, as can be seen by comparing the rate constant data of Comparative Example 2 with those of Example 1 or Example 4, the use of a guanidinium salt in the dehydrochlorination process affords much higher conversion rates without loss of selectivity in the final product.