CATALYTIC HYDROGENATION PROCESS FOR THE SYNTHESIS OF TERMINAL DIOLS FROM TERMINAL DIALKYL ALIPHATIC ESTERS

Abstract

A phosphorus ligand-free, mild, efficient and complete catalytic hydrogenation process is for the sustainable production of terminal diols from renewable terminal dialkyl esters with improved yield. Soluble, phosphorus ligand free Ru (II)-pincer type complexes can be used as catalysts in the hydrogenation process.

Claims

1. A catalytic hydrogenation process for synthesis of terminal diols starting from terminal dialkyl aliphatic esters, comprising, stirring a reaction mixture of phosphorus free catalyst, potassium tert-butoxide (.sup.tBuOK), terminal dialkyl aliphatic esters and toluene at temperature of 110° C. for a period in the range of 22 to 24 hr under H.sub.2 pressure, wherein said catalyst is selected from the group consisting of HCl(CO)Ru(.sup.isoPrSNS) (2), HCl(CO)Ru(.sup.PhSNS) (4), and HCl(CO)Ru(.sup.EtSNS) (5), represented by the formula ##STR00029##

2. The process as claimed in claim 1, wherein said terminal dialkyl aliphatic ester is selected from the group consisting of dialkyl oxalate, dialkyl malonate, dialkyl succinate, diethyl glutarate and dialkyl adipate, wherein alkyl groups in said terminal dialkyl aliphatic ester is linear or branched.

3. The process as claimed in claim 1, wherein said terminal diol is selected from the group consisting of ethane-1,2-diol, propane-1,3-diol, butane-1,4-diol, pentane-1,5-diol, and hexane-1,6-diol.

4. The process as claimed in claim 1, wherein a yield of said terminal diols is in the range of 35-70%.

5. A phosphorus-free catalyst of formula 4: ##STR00030##

6. A process for the preparation of phosphorus free catalyst of formula 2, 4 or 5, wherein said process comprises: (a) adding a methanolic solution of sodium thiolate compound and potassium hydroxide (KOH) to a solution of bis (2-chloroethyl)amine hydrochloride in methanol followed by stirring for 12 to 14 hrs at 30° C. to afford corresponding SNS compounds; and (b) refluxing the reaction mixture of compound of step (a), RuHCl(CO)(PPh.sub.3).sub.3 and o-xylene at temperature ranging from 140 to 150° C. for a period ranging from 1 to 2 hr under argon atmosphere to yield Ru (II)-pincer type SNS complexes.

7. The process as claimed in claim 6, wherein said sodium thiolate compound is selected from the group consisting of sodium-2-propanethiolate, sodium thiophenolate and sodium ethanethiolate.

8. The process as claimed in claim 6, wherein said SNS compounds are selected from the group consisting of bis (2-(phenylthio) ethyl) amine [.sup.PhSNS] (3), bis(2-(isopropylthio)ethyl)amine [.sup.isoPrSNS] (1) and bis (2-(ethylthio) ethyl) amine [.sup.EtSNS].

9. The process as claimed in claim 6, wherein said Ru (II)-pincer type SNS complexes is selected from the group consisting of HCl(CO)Ru(.sup.isoPrSNS) (2), HCl(CO)Ru(.sup.PhSNS) (4), and HCl(CO)Ru(Et-SNS) (5).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0042] The invention will now be described in detail in connection with certain preferred and optional embodiments, so that various aspects thereof may be more fully understood and appreciated.

[0043] In the view of above, the present invention provide a single step catalytic hydrogenation process for the synthesis of terminal diols from terminal dialkyl aliphatic esters using a phosphorus free catalyst comprising soluble Ru (II)-pincer type complexes.

[0044] In a preferred embodiment, the present invention provides a single step catalytic hydrogenation process for the synthesis of terminal diols starting from terminal dialkyl aliphatic esters comprises stirring the reaction mixture of phosphorus free catalyst, potassium tert-butoxide (.sup.tBuOK), terminal dialkyl aliphatic esters and toluene at temperature of about 110° C. for the period in the range of 22-24 hr under H.sub.2 pressure, characterized in that the yield of said terminal diols is in the range of 35-70%.

[0045] In preferred embodiment, said phosphorus ligand free catalyst is selected from Ru (II)-pincer type complexes of formula I, II and III.

[0046] In preferred embodiment, said catalyst is selected from HCl(CO)Ru(.sup.isoPrSNS) (2), HCl(CO)Ru(.sup.PhSNS) (4) and and RuHCl(CO)(.sup.EtSNS) (5).

[0047] In yet another preferred embodiment, said terminal dialkyl aliphatic ester is selected from dialkyl oxalate, dialkyl malonate, dialkyl succinate, diethyl glutarate, dialkyl adipate and said alkyl group may be linear or branched.

[0048] In still another preferred embodiment, said terminal diol is selected from ethane-1,2-diol, propane-1,3-diol, butane-1,4-diol, pentane-1,5-diol, and hexane-1,6-diol.

[0049] The one step catalytic hydrogenation process for the synthesis of terminal diols from dialkyl aliphatic esters is as shown in scheme 1 below:

##STR00006##

[0050] In another embodiment, the present invention provide a process for the synthesis 1,3-propanediol (1,3-PDO) from renewable dialkyl malanotes. The reaction is catalyzed by a soluble, phosphorus ligand free Ru (II)-pincer type complexes under mild condition (low hydrogen pressure and low temperature).

[0051] In another preferred embodiment, the present invention provides a single step catalytic hydrogenation process for the synthesis of 1,3-propanediol (1,3-PDO) starting from from renewable dialkyl malanotes comprises stirring the reaction mixture of catalyst, potassium tert-butoxide (.sup.tBuOK), dialkyl malanotes and toluene at temperature of about 110° C. for the period in the range of 22-24 hr under H.sub.2 pressure, characterized in that the yield of 1,3-propanediol (1,3-PDO) is 67%.

[0052] The process for the synthesis of 1,3-propanediol (1,3-PDO) from renewable dialkyl malanotes is as shown in scheme 2 below:

##STR00007##

[0053] The process yield for the catalytic hydrogenation of diethyl malonate to 1,3-propanediol (1,3-PDO) catalyzed by a soluble, phosphorus ligand free Ru (II)-pincer type complexes at different temperature and pressure is summarized in table 1:

TABLE-US-00001 TABLE 1 Reaction condition Sr. No. Catalyst Solvent Temp. (° C.) PH.sub.2 (atm) Yield (%).sup.a 1 2 THF 80 4.7 atm 21 2 2 toluene 110 4.7 atm 38 3 2 toluene 110 6.8 atm 67 4 4 toluene 110 6.8 atm 42 5 5 toluene 110 6.8 atm 51 .sup.aYield of products (ethanol) were analyzed by GC.

[0054] In an embodiment, the present invention provides novel catalysts of formula (I) (II) and (III);

##STR00008##

wherein; [0055] M is a noble or transition metal, X is S; [0056] R is isopropyl, ethyl, phenyl (which may be further substituted and selected from the group consisting of alkyl (linear and branched), halogen, trifluromethyl, nitro, amide, ester (—CO.sub.2R, —OC(O)R, —OC(O)CF.sub.3, —OSO.sub.2R, —OSO.sub.2CF.sub.3) cyano, alkoxy, alkylamino (mono or di), arylamino (mono or di), —SR, an inorganic support and a polymeric moiety) or ethyl.

[0057] A and B are each independently H or HBH.sub.3 or an anionic ligand selected from the group consisting of H, halogen, OCOR.sup.a, OCOCF.sub.3, OSO.sub.2R.sup.a, OSO.sub.2CF.sub.3, CN, OR.sup.a, N(R.sup.a).sub.2 and R.sup.aS.

[0058] L is a mono-dentate two-electron donor selected from the group consisting of CO, nitrile (RCN), isonitrile (RNC), N.sub.2, CS, heteroaryl, tetrahydrothiophene, alkene and alkyne. R.sup.a is each independently alkyl (linear and branched), cycloalkyl, aryl, heterocyclyl, heteroaryl, alkylcycloalkyl, alkylaryl, alkylheterocyclyl, alkylheteroaryl.

[0059] In one embodiment, the present invention provides a phosphorus free catalyst of formula 4;

##STR00009##

[0060] In another embodiment, the present invention provides a process for the preparation of phosphorus free catalyst of formula 2 and 4 and 5,

##STR00010##

wherein said process comprising the steps of: [0061] a) Adding a methanolic solution of sodium thiolate compound and potassium hydroxide (KOH) to a solution of bis (2-chloroethyl)amine hydrochloride in methanol followed by stirring for 12 to 14 hrs at 30° C. to afford corresponding SNS compound. [0062] b) Refluxing the reaction mixture of compound of step (a), RuHCl(CO)(PPh.sub.3).sub.3 (Carbonylchlorohydridotris (triphenylphosphino) ruthenium(II)) and o-xylene at temperature ranging from 140 to 150° C. for the period ranging from 1 to 2 hr under argon atmosphere to afford desired Ru (II)-pincer type SNS complex.

[0063] In preferred embodiment, said sodium thiolate compound is selected from sodium-2-propanethiolate, sodium thiophenolate and sodium ethanethiolate.

[0064] In another preferred embodiment, said SNS compound is selected from bis(2-(isopropylthio)ethyl)amine [.sup.isoPrSNS] (1), bis (2-(phenylthio)ethyl)amine [.sup.PhSNS] (3) and bis (2-(ethylthio) ethyl) amine [.sup.EtSNS].

[0065] In yet another preferred embodiment, said Ru (II)-pincer type SNS complexes is selected from HCl(CO)Ru(.sup.isoPrSNS) (2), RuHCl(CO)(Ph-SNS) (4), and RuHCl(CO)(.sup.EtSNS) (5).

[0066] The following examples, which include preferred embodiments, will serve to illustrate the practice of this invention, it being understood that the particulars shown are by way of example and for purpose of illustrative discussion of preferred embodiments of the invention.

EXAMPLES

Example 1

Hydrogenation of Aliphatic Diesters to Terminal Diols

[0067] ##STR00011##

[0068] A 90 mL Fischer-Porter tube was charged under nitrogen with catalyst (0.01 mmol), .sup.tBuOK (0.01 mmol), dialkyl esters (1.0 mmol), and toluene (2 mL). The Fischer-Porter tube was purged by three successive cycles of pressurization/venting with H.sub.2 (15 psi), then pressurized with H.sub.2 (6.8 atm). The solution was heated at 110° C. (bath temperature) with stirring for 24 hr. After cooling to ˜5° C. (ice/water), the excess H.sub.2 was vented carefully and the products were determined by GC using m-xylene as an internal standard.

[0069] The data comprising catalytic hydrogenation of aliphatic diesters to terminal diols is summarized in Table 2.

TABLE-US-00002 TABLE 2 Sr. Cata- No lyst Diester Products (yield %) 1 2 [00012] [00013] 2 2 [00014] [00015] 3 2 [00016] [00017] 4 2 [00018] [00019] 5 4 [00020] [00021] 5 5 [00022] [00023]

Example 2

Synthesis of 1,3-propanediol (1,3-PDO)

[0070] A 90 mL Fischer-Porter tube was charged under nitrogen with catalyst (0.01 mmol), .sup.tBuOK (0.01 mmol), diethyl malonate (1.0 mmol), and solvent (2 mL). The Fischer-Porter tube was purged by three successive cycles of pressurization/venting with H.sub.2 (15 psi), then pressurized with H.sub.2 (see table 3). The solution was heated at 80 or 110° C. (bath temperature) with stirring for 24 hr. After cooling to ˜5° C. (ice/water), the excess H.sub.2 was vented carefully and the products were (1,3-PDO and EtOH) determined by GC using m-xylene as an internal standard.

##STR00024##

TABLE-US-00003 TABLE 3 Catalytic hydrogenation of diethyl malonate to 1,3-propanediol (1,3-PDO). Reaction condition Sr. No. Catalyst Solvent Temp. (° C.) PH.sub.2 (atm) Yield (%).sup.a 1 2 THF 80 4.7 atm 21 2 2 toluene 110 4.7 atm 38 3 2 toluene 110 6.8 atm 67 4 4 toluene 110 6.8 atm 42 5 5 toluene 110 6.8 atm 51 .sup.aYield of products (ethanol) were analyzed by GC.

Example 3a

Synthesis of .SUP.isoPr.SNS (1)

[0071] ##STR00025##

[0072] An oven-dried 50 mL round bottom flask equipped with a stirring bar and dropping funnel was cooled under a stream of nitrogen. The flask was then charged with bis(2-chloroethyl)amine hydrochloride (4.46 g, 25.00 mmol) 15 mL of distilled methanol. A methanol solution (20 mL) of sodium-2-propanethiolate (5.45 g, 55.50 mmol) and KOH (30 mmol) was added dropwise during 10 min. Then the mixture was stirred for 12 hrs at 30° C. The solvent was removed under reduced pressure to give yellow slurry and the product was extracted with 3×15 mL of hexane. The combined hexane solutions were removed under vacuum to get oily liquid. This was purified by column chromatography (neutral alumina; petroleum ether: ethyl acetate (20:1) as eluent) to yield 4.54 g (82%) of bis(2-(isopropylthio)ethyl)amine [.sup.isoPrSNS] (1).

[0073] .sup.1H NMR (200 MHz, CDCl.sub.3): δ 2.87 (m, J=6.0 Hz, 2H, CH), 2.76 (t, J=6.0 Hz, 4H, NHCH.sub.2), 2.63 (t, J=6.0 Hz, 4H, SCH.sub.2), 1.77 (br s, 1H, NH), 1.22 (d, J=6.0 Hz, 12H, CH.sub.3). .sup.13C{.sup.1H} NMR (100 MHz, CDCl.sub.3): δ 48.8 (s, 2C, NCH.sub.2), 34.8 (s, 2C, CH), 30.8 (s, 2C, SCH.sub.2), 23.6 (s, 4C, CH.sub.3). HRMS (FAB) Calculated for C.sub.10H.sub.23NS.sub.2 [MH.sup.+]: 222.1350. Found: 222.1345.

Example 3b

Synthesis of HCl(CO)Ru(.SUP.isoPr.SNS) (2)

[0074] ##STR00026##

[0075] To an oven dried 20 mL schlenk tube equipped with magnetic stirring bar was added bis (2-(isopropylthio) ethyl) amine [.sup.isoPrSNS] (220 mg, 0.94 mmol), RuHCl(CO)(PPh.sub.3).sub.3 (0.85 mmol), and 8 mL dry o-xylene under argon atmosphere. The reaction mixture was refluxed under argon atm in a preheated oil bath maintained at 140° C. for 1 hr, then cooled to room temperature to lead to precipitation of a greenish-yellow solid. The solvent was decanted and the solid thus obtained was washed with ether (3×5 mL), then dried under vacuum to give RuHCl(CO)(.sup.isoPr-SNS) (210 mg, 54%).

[0076] IR (KBr pellet, cm.sup.−1): 1924, 1960, 3165. .sup.1H NMR (200 MHz, CD.sub.2Cl.sub.2): δ 4.43 (br s, NH), 3.73-3.35 (m, 4H, CH.sub.2), 3.08-2.92 (m 2H, CH), 2.87-2.59 (m, 4H, CH.sub.2), 1.47-1.36 (m, 12H, CH.sub.3), −16.60 (s, 17%, RuH), −17.11 (s, 62%, RuH), −17.65 (s, 21%, RuH). .sup.13C{.sup.1H} NMR (100 MHz, CD.sub.2Cl.sub.2): a mixture of isomers δ 205.5 (br s, CO), 52.2 and 52.1 (2s, NCH.sub.2), 51.2 and 50.9 (2s, NCH.sub.2), 43.9 and 43.4 (2s, SCH(CH.sub.3).sub.2), 41.4 and 40.7 (2s, SCH(CH.sub.3).sub.2), 39.6 and 39.3 (2s, SCH.sub.2), 36.6 and 36.7 (2s, SCH.sub.2), 21.8 and 21.9 (2s, CH(CH.sub.3).sub.2), 21.5 (br s, CH(CH.sub.3).sub.2), 21.3 and 21.2 (2s, CH(CH.sub.3).sub.2), 21.03 and 20.93 (2s, CH(CH.sub.3).sub.2). HRMS (FAB) Calculated for C.sub.11H.sub.24NORuS.sub.2 [M-Cl].sup.+: 352.0343. Found: 352.0330.

Example 4a

Synthesis of .SUP.Ph.SNS (3)

[0077] ##STR00027##

[0078] An oven-dried 50 mL round bottom flask equipped with a stirring bar and dropping funnel was cooled under a stream of nitrogen. The flask was then charged with bis (2-chloroethyl)amine hydrochloride (4.46 g, 25.00 mmol) 15 mL of distilled methanol. A methanol solution (20 mL) of sodium thiophenolate (4.77 g, 55.50 mmol) and KOH (30 mmol) was added dropwise during 10 min. Then the mixture was stirred for 12 hrs at 30° C. The solvent was removed under reduced pressure to give yellow slurry and the product was extracted with 3×15 mL of hexane. The combined hexane solutions were removed under vacuum to get oily liquid. This was purified by column chromatography (neutral alumina; petroleum ether: ethyl acetate (20:1) as eluent) to yield 5.86 g (81%) of bis (2-(phenylthio) ethyl) amine[.sup.PhSNS] (3).

[0079] .sup.1H NMR (200 MHz, CDCl.sub.3): δ 7.38-7.15 (m, 10H, Phenyl-H), 3.04 (br d, J=8 Hz, 4H, SCH.sub.2), 2.83 (br d, J=8 Hz, 4H, NHCH.sub.2). .sup.13C{.sup.1H} NMR (100 MHz, CDCl.sub.3): δ 135.7 (s, 2C, SCH.sub.2), 129.9 (s, 4C, ortho-(C)Ph), 129.1 (s, 4C, meta-(C)Ph), 126.1 (s,2C, para-(C)Ph), 47.8 (s, 2C, NHCH.sub.2), 34.3 (s, 2C, SCH.sub.2). HRMS (FAB) Calculated for C.sub.16H.sub.20NS.sub.2 [MH+]: 290.1037. Found: 290.1032.

Example 4b

Synthesis of HCl(CO)Ru(.SUP.Ph.SNS) (4)

[0080] ##STR00028##

[0081] To an oven dried 20 mL schlenk tube equipped with magnetic stirring bar was added bis(2-(phenylthio)ethyl)amine [.sup.PhSNS] (272 mg, 0.94 mmol), RuHCl(CO)(PPh.sub.3).sub.3 (0.85 mmol), and 8 mL dry o-xylene under argon atmosphere. The reaction mixture was refluxed under argon atm in a preheated oil bath maintained at 150° C. for 2 hr, then cooled to room temperature to form a reddish brown precipitate. The solvent was decanted and the solid thus obtained was washed with ether (3×5 mL), then dried under vacuum to give analytically pure complex RuHCl(CO)(.sup.PhSNS) (318 mg, 70%).

[0082] HRMS (FAB) Calculated for C.sub.17H.sub.20NORuS.sub.2 [M-Cl].sup.+: 420.0030. Found: 420.0023.

ADVANTAGES OF THE INVENTION

[0083] Environmentally benign approach. [0084] Cheap and easily available raw materials used. [0085] Simple and cost-effective process. [0086] Single step process with improved yield.