Process for the preparation of liquid tin(II) alkoxides
09637507 ยท 2017-05-02
Assignee
Inventors
- Puttinan Meepowpan (Mueang Chiang Mai, TH)
- Winita Punyodom (Mueang Chiang Mai, TH)
- Robert Molloy (Mueang Chiang Mai, TH)
Cpc classification
C07F7/2224
CHEMISTRY; METALLURGY
International classification
Abstract
A synthetic process of producing liquid tin(II) alkoxides for use as either catalysts in the synthesis of lactide or as initiators in the polymerization of cyclic ester monomers to yield biodegradable polyesters is described. The synthetic process employs anhydrous tin(II) chloride dissolved in n-heptane mixed with dry diethylamine. Alcohols, ROH, in which the R groups are n-C.sub.4H.sub.9, n-C.sub.6H.sub.13, and n-C.sub.8H.sub.17 are added to the reaction mixture and stirred for 12 hours. The reaction mixture is then filtered under nitrogen or argon before being evaporated to dryness to yield the three tin(II) alkoxides, namely: tin(II) n-butoxide, tin(II) n-hexoxide, and tin(II) n-octoxide. All three tin(II) alkoxides are viscous, dark yellow liquids which are highly soluble in most common organic solvents. Furthermore, they can all be stored under an inert atmosphere for long periods without any significant change in their reactivity and, therefore, in their effectiveness as catalysts/initiators.
Claims
1. A process for producing a tin(II) alkoxide, comprising steps of: adding one mole equivalent of anhydrous tin(ll) chloride to a reaction vessel; adding 2 to 3 mole equivalents of an amine to the reaction vessel of the anhydrous tin(ll) chloride in a nonpolar, aprotic solvent; further adding 2 to 3 mole equivalents of anhydrous alcohol ROH to the reaction vessel to provide a reaction mixture such that a newly produced tin(ll) alkoxide Sn(OR).sub.2 does not undergo self-aggregation; stirring the reaction mixture for at least 3 hours in a temperature range of 25- 38 C. to provide a tin(ll) alkoxide Sn(OR).sub.2, wherein the R group is selected from the group comprising CH.sub.3, C.sub.2H.sub.5, nC.sub.3H.sub.7, nC.sub.4H.sub.9, nC.sub.5H.sub.11, nC.sub.6H.sub.13, nC.sub.7H.sub.15, and nC.sub.8H.sub.17 and the steps are carried out under inert atmosphere; wherein the amine is selected from the group consisting of dimethylamine, diethylamine and diisopropylamine.
2. The process of claim 1, wherein the amine comprises diethylamine.
3. The process of claim 1, wherein the nonpolar, aprotic solvent is selected from the group consisting of n-heptane, n-hexane, cyclohexane, benzene, toluene, xylene, and tetrahydrofuran.
4. The process of claim 3, wherein the nonpolar, aprotic solvent comprises n-heptane.
5. The process of claim 1, wherein the nonpolar, aprotic solvent is dry n-heptane; further comprising steps of: adding dry n-heptane to the reaction vessel prior to addition of the anhydrous tin(II) chloride; dissolving the anhydrous tin(II) chloride in the dry n-heptane; maintaining a temperature range of 25-38 C. of the reaction mixture during addition of anhydrous alcohol ROH; stirring the reaction mixture for about 12 hours; filtering the reaction mixture to obtain a solid residue; washing the solid residue with dry n-heptane; evaporating a combined filtrate to dryness, wherein the inert atmosphere is nitrogen or argon atmosphere.
6. A process for producing a tin(II) alkoxide, comprising steps of: dissolving one mole equivalent of anhydrous tin(II) chloride in dry n-heptane in a reaction vessel in a temperature range of 25-38 C., wherein a resultant solution is stirred for 30-60 minutes; adding 2 to 3 mole equivalents of diethylamine to the reaction vessel of the anhydrous tin(II) chloride in the temperature range of 15-20 C., wherein the resultant solution is stirred for 36 hours; further adding 2 to 3 mole equivalents of anhydrous alcohol ROH to the reaction vessel to provide a reaction mixture such that a newly produced tin(II) alkoxide Sn(OR).sub.2 does not undergo self-aggregation; stirring the reaction mixture for about 12 hours in a temperature range of 25-38 C.; filtering the reaction mixture to obtain a solid residue; washing the solid residue with dry n-heptane; evaporating a combined filtrate to dryness to provide a tin(II) alkoxide Sn(OR).sub.2, wherein the R group is selected from the group comprising nC.sub.4H.sub.9, nC.sub.6H.sub.13, nC.sub.8H.sub.17 and the steps are carried out under nitrogen or argon atmosphere.
Description
BRIEF DESCRIPTION OF DRAWINGS
(1) For a fuller understanding of the invention, reference is made to the following description, taken in connection with the accompanying drawings, in which:
(2)
(3)
(4)
(5)
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
(6) This invention describes the development of the synthetic process of liquid tin(II) alkoxides which are soluble in organic solvents for the preparation of lactide and polyesters by using anhydrous tin(II) chloride instead of tin(II) chloride dehydrate, 2) changing from triethylamine to diethylamine or other amines such as dimethylamine, diisopropylamine, and trimethyl-amine as a base or ligand to enhance the nucleophilicity on the substitution of chlorine atoms, resulting in the formation of SnCl.sub.2.HNEt.sub.2 in high yield, as shown in the following equation:
(7) ##STR00007##
(8) This also allows the alcohol to react with the tin atom of SnCl.sub.2.HNEt.sub.2 better than that of SnCl.sub.2.NEt.sub.3. Finally, 3) by using one of the following nonpolar aprotic solvents: n-heptane, n-hexane, cyclohexane, benzene, toluene, xylene, and tetrahydrofuran instead of an excess of a polar, protic solvent such as an alcohol., the nonpolar aprotic solvent molecules can surround the molecules of tin(II) alkoxide, thereby preventing their self-aggregation. If excess alcohol is used, it can result in the formation of tin(II) alkoxide with bridging alcohol molecules leading to the poor solubility of tin(II) alkoxide in most common organic solvents. Moreover, the use of nonpolar aprotic solvents causes the precipitation of Et.sub.2NH.HCl from the soluble tin(II) alkoxide so that purification of tin(II) alkoxide prior to use is not necessary.
(9) The objective of the synthetic process of liquid tin(II) alkoxides is to obtain products which can act as reagents in the synthesis of lactides such as l-lactide, d-lactide, and dl-lactide and as initiators in the synthesis of polyesters from cyclic esters such as polylactide, poly-(-caprolactone), polyglycolide, and co-polyesters. This procedure is the first successful process to produce liquid tin(II) alkoxides with no such procedure having yet been reported in the literature. All three tin(II) alkoxides: tin(II) n-butoxide (Sn(O-n-C.sub.4H.sub.9).sub.2), tin(II) n-hexoxide (Sn(O-n-C.sub.6H.sub.13).sub.2), and tin(II) n-octoxide (Sn(O-n-C.sub.8H.sub.17).sub.2), which were synthesized from this process, are viscous, dark yellow liquids. They could be mixtures of monomer, dimer, trimer, and/or oligomers that are still soluble in common organic solvents in the temperature range of 25-38 C. They can be stored under a nitrogen or argon atmosphere without any significant effect on their reactivity. Moreover, the products from this process do not require any further purification and can be used either as a reagent or initiator in the solution phase.
(10) The synthetic process of liquid tin(II) alkoxides in this invention is composed of several important steps which are 1) the use of anhydrous tin(II) chloride instead of tin(II) chloride dihydrate, 2) the use of dimethylamine, diisopropylamine, trimethylamine or triethylamine in the 2.0-2.1 mole equivalence of anhydrous tin(II) chloride to enhance the nucleophilicity or ligand ability in the substitutions of chloride compared to the use of triethylamine, resulting in the formation of SnCl.sub.2.HNEt.sub.2 in high yield and giving a better reaction between the alcohol molecule and the tin atom of SnCl.sub.2.HNEt.sub.2 than that of SnCl.sub.2.NEt.sub.3, and most importantly, 3) the use of one of the suggested nonpolar aprotic solvents such as n-heptane, n-hexane, cyclohexane, benzene, toluene, xylene, and tetrahydrofuran instead of polar protic solvents such as alcohols to inhibit the formation of tin(II) alkoxide self-aggregates. Moreover, nonpolar aprotic solvent also allow for the precipitation and therefore easy separation of Et.sub.2NH.HCl from the tin(II) alkoxide in solution. Thus, no further purification of tin(II) alkoxide is required; 4) the amount of alcohol used in this process is about 2.0-2.1 mole equivalence of the anhydrous tin(II) chloride to reduce the aggregation of tin(II) alkoxide in the presence of excess alcohol.
(11) Examples 1 for chemicals used in process for the preparation of liquid tin(II) alkoxides (Sn(OR).sub.2) are:
(12) 1. Anhydrous tin(II) chloride, purity >98%, purchased from Aldrich. Molecular weight=189.62 g/mol, boiling point=652 C., and melting point=246 C.
(13) 2. Diethylamine ((C.sub.2H.sub.5)NH). Molecular weight=73.14 g/mol, boiling point=55 C., melting point=50 C., density=0.707 g/mL (25 C.). Must be purified by refluxing with sodium (Na) or calcium hydride (CaH.sub.2) for 1 hour and distilled prior to use. Dry diethylamine is kept under nitrogen or argon, or kept in a container with molecular sieves.
(14) 3. N-butanol (n-C.sub.4H.sub.9OH). Molecular weight=74.12 g/mol, boiling point=116-118 C., melting point=90 C., density=0.81 g/mL (25 C.). Must be purified by refluxing with sodium (Na) for 1 hour and distilled prior to use. Dry n-butanol is kept under nitrogen or argon, or kept in a container with molecular sieves.
(15) 4. N-hexanol (n-C.sub.6H.sub.13OH). Molecular weight=102.17 g/mol, boiling point=156-157 C., melting point=52 C., density=0.814 g/mL (25 C.). Must be purified by refluxing with sodium (Na) for 1 hour and distilled prior to use. Dry n-hexanol is kept under nitrogen or argon, or kept in a container with molecular sieves.
(16) 5. N-octanol (n-C.sub.8H.sub.17OH). Molecular weight=130.23 g/mol, boiling point=196 C., melting point=15 C., density=0.827 g/mL (25 C.). Must be purified by refluxing with sodium (Na) for 1 hour and distilled prior to use. Dry n-octanol is kept under nitrogen or argon, or kept in a container with molecular sieve.
(17) 6. N-heptane (n-C.sub.7H.sub.16). Molecular weight=100.20 g/mol, boiling point=98 C., melting point=91 C., density=0.684 g/mL (25 C.). Must be purified by refluxing with sodium (Na) for 1 hour and distilled prior to use. Dry n-heptane is kept under nitrogen or argon, or kept in a container with molecular sieves.
(18) To fully understand this invention, the following further details are given:
(19) Example 2 for the preparation of liquid tin(II) n-butoxide (Sn(O-n-C.sub.4H.sub.9).sub.2)
(20) 1. A three-necked round bottom flask is equipped with a magnetic bar, an oven-dried gas-inlet, and a dropping funnel. It is placed on a magnetic stirrer. A gas-inlet is connected to a volumetric gauge-controlled nitrogen or argon source via a plastic tube.
(21) 2. Anhydrous tin(II) chloride 4.84 g (25.01 mmol) is added to the reaction flask.
(22) 3. Dry n-heptane (ca. 100 mL) is added into the reaction vessel at the temperature range of 25-38 C. The mixture was well-stirred for 30-60 minutes.
(23) 4. Dry diethylamine (5.43 mL, 52.53 mmol) is then added into the reaction vessel in the temperature range of 15-20 C. The reaction mixture is stirred for 3-6 hours.
(24) 5. Solution of dry n-butanol 4.81 mL (52.53 mmol) in dry n-heptane (ca. 50 mL) was added to the reaction mixture in the temperature range of 25-38 C. The resulting solution is stirred for another 12 hours.
(25) 6. The reaction mixture is filtered under nitrogen or argon, and the solid residue is thoroughly washed with dry n-heptane (100-200 mL).
(26) 7. The filtrate is concentrated and evaporated to dryness on a rotary evaporator.
(27) 8. The residue of tin(II) n-butoxide is further dried using a high vacuum pump for another 3-6 hours.
(28) 9. Tin(II) n-butoxide is obtained as viscous, dark yellow liquid, in 4.89 g, 73.79% yield.
(29) Example 3 for the preparation of liquid tin(II) n-hexoxide (Sn(O-n-C.sub.6H.sub.13).sub.2)
(30) 1. A three-necked round bottom flask is equipped with a magnetic bar, an oven-dried gas-inlet, and a dropping funnel. It is placed on a magnetic stirrer. A gas-inlet is connected to a volumetric gauge-controlled nitrogen or argon source via a plastic tube.
(31) 2. Anhydrous tin(II) chloride 4.84 g (25.01 mmol) is added to the reaction flask.
(32) 3. Dry n-heptane (ca. 100 mL) is added into the reaction vessel at the temperature range of 25-38 C. The mixture was well-stirred for 30-60 minutes.
(33) 4. Dry diethylamine (5.43 mL, 52.53 mmol) is then added into the reaction vessel in the temperature range of 15-20 C. The reaction mixture is stirred for 3-6 hours.
(34) 5. Solution of dry n-hexanol 6.59 mL (52.53 mmol) in dry n-heptane (ca. 50 mL) was added to the reaction mixture in the temperature range of 25-38 C. The resulting solution is stirred for another 12 hours.
(35) 6. The reaction mixture is filtered under nitrogen or argon, and the solid residue is thoroughly washed with dry n-heptane (100-200 mL).
(36) 7. The filtrate is concentrated and evaporated to dryness on a rotary evaporator.
(37) 8. The residue of tin(II) n-hexoxide is further dried using a high vacuum pump for another 3-6 hours.
(38) 9. Tin(II) n-hexoxide is obtained as viscous, dark yellow liquid, in 6.97 g, 86.73% yield.
(39) Example 4 for the preparation of liquid tin(II) n-octoxide (Sn(O-n-C.sub.8H.sub.17).sub.2)
(40) 1. A three-necked round bottom flask is equipped with a magnetic bar, an oven-dried gas-inlet, and a dropping funnel. It is placed on a magnetic stirrer. A gas-inlet is connected to a volumetric gauge-controlled nitrogen or argon source via a plastic tube.
(41) 2. Anhydrous tin(II) chloride 4.84 g (25.01 mmol) is added to the reaction flask.
(42) 3. Dry n-heptane (ca. 100 mL) is added into the reaction vessel at the temperature range of 25-38 C. The mixture was well-stirred for 30-60 minutes.
(43) 4. Dry diethylamine (5.43 mL, 52.53 mmol) is then added into the reaction vessel in the temperature range of 15-20 C. The reaction mixture is stirred for 3-6 hours.
(44) 5. Solution of dry n-octanol 8.27 mL (52.53 mmol) in dry n-heptane (ca. 50 mL) was added to the reaction mixture in the temperature range of 25-38 C. The resulting solution is stirred for another 12 hours.
(45) 6. The reaction mixture is filtered under nitrogen or argon, and the solid residue is thoroughly washed with dry n-heptane (100-200 mL).
(46) 7. The filtrate is concentrated and evaporated to dryness on a rotary evaporator.
(47) 8. The residue of tin(II) n-octoxide is further dried using a high vacuum pump for another 3-6 hours.
(48) 9. Tin(II) n-octoxide is obtained as viscous, dark yellow liquid, in 7.00 g, 74.18% yield.
(49) Products from the syntheses of liquid tin(II) alkoxides, their molecular formula, physical appearances, percentage yields and solubilities are summarized in
(50) TABLE-US-00004 TABLE 4 Molecular formula, physical appearances, and percentage yields of tin(II) alkoxides. Tin(II) Percent alkoxide Molecular formula Physical appearances yield Tin(II) Sn(On-C.sub.4H.sub.9).sub.2 Viscous, dark yellow liquid 73.79 n-butoxide Tin(II) Sn(On-C.sub.6H.sub.13).sub.2 Viscous, dark yellow liquid 86.73 n-hexoxide Tin(II) Sn(On-C.sub.8H.sub.17).sub.2 Viscous, dark yellow liquid 74.18 n-octoxide
(51) TABLE-US-00005 TABLE 5 Solubilities of liquid tin(II) alkoxides in various organic solvents. Chloroform/ Methanol/ toluene/ acetone/ Dimethyl sulfoxide/ Tin(II) alkoxide n-heptane tetrahydrofuran o-dichlorobenzene Tin(II) n-butoxide x x Tin(II) n-hexoxide x x Tin(II) n-octoxide x x Note: x is insoluble even when heated. is soluble at room temperature.
(52) IR characterization data of the liquid tin(II) alkoxides synthesized as described in the invention compared with that of solid tin(II) alkoxides are shown in
(53) TABLE-US-00006 TABLE 6 IR characterization data of liquid tin(II) alkoxides and their respective solid forms. Wavenumber (, cm.sup.1) Sn(O-n-C.sub.4H.sub.9).sub.2 Sn(O-n-C.sub.6H.sub.13).sub.2 Sn(O-n-C.sub.8H.sub.17).sub.2 Assignment Solid* Liquid Solid* Liquid Solid* Liquid CH.sub.3 2911 (w) 2956 (s) 2911 (w) 2950 (s) 2911 (w) 2953 (s) 2862 (s) CH.sub.2 2922 (s) 2925 (s) 2922 (s) 2851 (s) 2858 (s) 2851 (s) CH.sub.3 (def) 1369 (m) 1377 (w) 1378 (m) 1377 (w) 1373 (m) CH.sub.2 (def) 1455 (m) 1455 (m) 1455 (m) CO 1014 (w) 1067 (m) 1007 (w) 1052 (m) 1007 (w) 1049 (m) (stretch) 1039 (m) 1025 (m) 1014 (m) SnOSn 740 (w) 740 (w) 740 (w) (stretch) SnO 541 (s) 573 (br s) 541 (s) 505 (br m) 541 (s) 581 (br m) (stretch) 512 (br s) 528 (br m) Note: *Solid tin(II) alkoxides were synthesized by the method reported by Morrison and Haendler. def = deformation; s = strong; m = medium; br = broad; w = weak
(54) Molecular weights of liquid tin(II) alkoxide analyzed by GC-MS and LC-MS techniques are tabulated in Table 7.
(55) TABLE-US-00007 TABLE 7 Molecular ions of liquid tin(II) alkoxides from GC-MS and LC-MS techniques. Found molecular Tin(II) alkoxide ion (m/z) Structure of found molecular ion Sn(On-C.sub.4H.sub.9).sub.2 264.sup. M.sup.+ = [Sn(OnC.sub.4H.sub.9).sub.2].sup.+ (MW = 264) 265.sup. [M + H].sup.+ = [Sn(OnC.sub.4H.sub.9).sub.2 + H].sup.+ 287.sup. [M + Na].sup.+ = [Sn(OnC.sub.4H.sub.9).sub.2 + Na].sup.+] Sn(On-C.sub.6H.sub.13).sub.2 320.sup. M.sup.+ = [Sn(OnC.sub.6H.sub.13).sub.2].sup.+ (MW = 320) 321 [M + H].sup.+ = [Sn(OnC.sub.6H.sub.13).sub.2 + H].sup.+ 343.sup. [M + Na].sup.+ = [Sn(OnC.sub.6H.sub.13).sub.2 + Na].sup.+] Sn(On-C.sub.8H.sub.17).sub.2 376.sup. M.sup.+ = [Sn(OnC.sub.8H.sub.19).sub.2].sup.+ (MW = 376) 377.sup. [M + H].sup.+ = [Sn(OnC.sub.8H.sub.19).sub.2 + H].sup.+ 399.sup. [M + Na].sup.+ = [Sn(OnC.sub.8H.sub.19).sub.2 + Na].sup.+] Note: .sup.is molecular ion from GC-MS. .sup.is molecular ion from LC-MS. .sup.1H-NMR characterization data are shown in FIG. 3 and Table 8, while the .sup.13C-NMR characterization data are summarized in FIG. 4 and Table 9.
(56) TABLE-US-00008 TABLE 8 .sup.1H-NMR data of liquid tin(II) alkoxides (400 MHz, CDCl.sub.3, 25 C.).
(57) TABLE-US-00009 TABLE 9 .sup.13C-NMR data of liquid tin(II) alkoxides (100 MHz, CDCl.sub.3, 25 C).
(58) In conclusion, the synthetic process for producing liquid tin(II) n-butoxide, tin(II) n-hexoxide, and tin(II) n-octoxide can be successfully accomplished via the following important steps: 1) enough diethylamine in 2 or 3 mole equivalence of anhydrous tin(II) chloride to act as a base or ligand in the formation of SnCl.sub.2.HNEt.sub.2 in high yield, and 2) the use of nonpolar aprotic solvents such as n-heptane instead of alcohols such as methanol and ethanol. Molecules of n-heptane can solvate the tin(II) alkoxide, thereby preventing its self-aggregation during the reaction. Another important advantage of using nonpolar aprotic solvent systems is that they facilitate the precipitation and separation of the Et.sub.2NH.HCl by-product from the soluble tin(II) alkoxide. Therefore, no further purification of the tin(II) alkoxide is required prior to its use as either a reagent or initiator. Finally, 3) the use of a suitable amount of alcohol of about 2-3 mole equivalence of the anhydrous tin(II) chloride can reduce the aggregation between the tin(II) alkoxide and the bridging alcohol. Tin(II) alkoxides produced from this process are viscous, dark yellow liquids, soluble in common organic solvents at room temperature, and can be stored for a long time under nitrogen or argon without any significant change in their reactivity. In addition, the products from the process can be used either as a reagent or an initiator without any extra purification and can be used either neat or in solution form.