CA1088956A - N-(2-mercaptoethyl)alkanamides from h 1n2 xxs and 2-h- 2-oxazolines or 2-alkyl-2-oxazolines - Google Patents
N-(2-mercaptoethyl)alkanamides from h 1n2 xxs and 2-h- 2-oxazolines or 2-alkyl-2-oxazolinesInfo
- Publication number
- CA1088956A CA1088956A CA298,231A CA298231A CA1088956A CA 1088956 A CA1088956 A CA 1088956A CA 298231 A CA298231 A CA 298231A CA 1088956 A CA1088956 A CA 1088956A
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- Prior art keywords
- oxazolines
- hydrogen
- alkyl
- mercaptoethyl
- reaction
- Prior art date
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- Heterocyclic Carbon Compounds Containing A Hetero Ring Having Nitrogen And Oxygen As The Only Ring Hetero Atoms (AREA)
Abstract
A B S T R A C T
The invention is directed to a process for preparing N-(2-mercaptoethyl)alkanamides by reacting hydrogen sulfide with 2-H-2-oxazolines or 2-alkyl-2--oxazolines. These prepared materials have utility as chemical intermediates, for example, all of them can be hydrolyzed with aqueous hydrogen chloride to prepare 2-mercaptoethylamine hydrochloride, which is useful when neutralized as a curing agent for epoxy resins, as an acid scavenger and as a pharmaceutical intermediate.
The invention is directed to a process for preparing N-(2-mercaptoethyl)alkanamides by reacting hydrogen sulfide with 2-H-2-oxazolines or 2-alkyl-2--oxazolines. These prepared materials have utility as chemical intermediates, for example, all of them can be hydrolyzed with aqueous hydrogen chloride to prepare 2-mercaptoethylamine hydrochloride, which is useful when neutralized as a curing agent for epoxy resins, as an acid scavenger and as a pharmaceutical intermediate.
Description
~- ~08~
The chemistry of oxazolines has been reviewed extensively in three major review articles: (1) Wiley et al., Chemical Reviews, Volume 44, 447(1949); (2) Seeliger et al., Angew. Chem. International Addition, Volume 5, No. 10, 875 (1966); and (3) Frump, Chemical Reviews, 1971, Volume 71, 5483. Such review articles indicate ~hat a wide variety of ring-opening reactions of oxazolines are known but surprisingly few reactions of hydrogen sulfide with oxazolines have ever been considered.
Tomalia et al., in U.S. Patent 3,670,046 ~aught that certain bisoxazolines react with bismercaptans or hydrogen sulfide to produce polymers. Tomalia et al.
also taught in U.S. Patents 3,~30,996, 3,723,451 and 3,746,691 that hydrogen sulfide reacts with certain
The chemistry of oxazolines has been reviewed extensively in three major review articles: (1) Wiley et al., Chemical Reviews, Volume 44, 447(1949); (2) Seeliger et al., Angew. Chem. International Addition, Volume 5, No. 10, 875 (1966); and (3) Frump, Chemical Reviews, 1971, Volume 71, 5483. Such review articles indicate ~hat a wide variety of ring-opening reactions of oxazolines are known but surprisingly few reactions of hydrogen sulfide with oxazolines have ever been considered.
Tomalia et al., in U.S. Patent 3,670,046 ~aught that certain bisoxazolines react with bismercaptans or hydrogen sulfide to produce polymers. Tomalia et al.
also taught in U.S. Patents 3,~30,996, 3,723,451 and 3,746,691 that hydrogen sulfide reacts with certain
2-alkenyl-2-oxazolines to produce the corresponding bis(2-oxazolinylethyl)sulfides. However, neither of these references mentions the preparation of N-(2-mercapto-ethyl)alkanamides.
It has now been discovered that N-t2-mercaptoethyl) alkanamides can be prepared in excellent yield by the present invention, which is a process for preparing an N-(2-mercapto-ethyl)alkanamide comprising reacting under anhydrous con-ditions (a) a 2-H-2-oxazoline or a 2-alkyl-2-oxazoline having the formula ¦ ~C - R
~ ~4 -17,732A-F -1-" ' ' :
1~8~9S6 wherein R is hydrogen or an alkyl group of from 1 to 18 carbon atoms and each of Rl to R4 are hydrogen, lower alkyl, hydroxy-substituted lower alkyl or phenyl, with (b) hydrogen sulfide.
Such products form a known class of useful compounds having many members, all of which can be hydrolyzed with aqueous ~HCl to form a 2-mercaptoethylamine hydrochloride which has utility, when neutralized, as an epoxy curing agent, as an acid scavenger and as a pharma-ceutical intermediate.
The reactants in the instant process are known classes of reactants. The 2-H-a-oxazolineS and 2-alkyl-2--oxazolines correspond to the formula Il :
¦ C - R
~.. .
in which R is hydrogen or an alkyl group of from 1 to 18 carbon atoms, and preferably R is methyl or ethyl. Each of Rl to R4 is hydrogen, lower alkyl (from 1 to 6 carbon atoms), hydroxy-substituted lower alkyl or phenyl. Pref-erably, Rl and R2 are hydrogen, methyl, ethyl or hydroxy-methyl and R3 and R4 are each hydrogen. Most preferably, Rl to R4 are each hydrogen.
Examples of suitable such 2-alkyl~2-oxazoline reactants include those of -formula I having the values of R and Rl to R4 set forth in Table I.
17,732A-F -2-.. .
- ~ . . : . . ' : ,' .: : , . ' : :, . :, . : .
r `~ lV~ 5~;
TABLE I
R Rl R2 R3 R~
H H H H H
C7H15 H ~ H H
CllH23 H H H H
C5HllC6H5 H H C6H5 C2H5 C~Hg ~ H C6H5 The 2-oxazolines used herein are normally prepared by reacting an alkanoic acid with an ethanolamine to form the corresponding acid/amine salt or amide, which in turn is heated in the presence of an aluminum oxide catalyst to form the corresponding 2-alkyl-2-oxazoline product.
The reaction may be conducted neat or in an organic solvent that is inert in the instant process.
Suitable such solvents include the lower alkanols and particularly methanol and combinations of such lower alkanols with conventional hydrocarbon solvents (e.g.
benzene, toluene, etc.). It is preferred to conduct the instant process neat or in methanol. It is also preferred to conduct the reaction under substantially anhydrous conditions. The 2-oxazolines are susceptible to hydrolysis 17,732~-F -3-by water and essentially anhydrous conditions are therefore required to optimize product yield.
The stoichiometry of the reaction requires 1 mole of hydrogen sulfide per mole of 2-alkyl-2--oxazoline reactant. More or less than the stoichio-metric amount of either reactant can be used. However, it is preferred to use an excess of hydrogen sulfide to effect $he completion of the reaction and to maximize the product yield at the expense of by-products, such as bis(alkanamidoethyl) sulfide.
The order of addition or method of blending the reactants is not critical. From a procedural standpoint, however, it is advantageous to add the hydrogen sulfide incrementally to a reaction vessel precharged with the -~
oxazoline reactant, mainly for effectively controlling the reaction temperature.
Substantially any reaction temperature of from about 20 to about 200C can be used but we normally prefer to conduct the reaction at a temperature of from about 50 to about 150C. At these temperatures, the reaction may be conducted under autogenous or superatmospheric pressures in conventional pressure equipment. The instant reaction is e~othermic and normally will not require additional heat after ~he reaction is star~ed. Normally, it is advantageous to conduct the reaction in equipment where the temperature can be controlled by cooling.
It has been observed that the reaction rate and product yields are lower when a reaction temperature in lower ranges are used (e.g. from about 20 to about 70).
17,732A~F _4_ .. ~ . ~.
95!6i In these instances the product yields can be increased by warming the reaction mixture to the preferred tem-perature range (e.g. 100-150C). This post-heating step appears to cause at least one of the by-products (e.g. a hydroxyethyl thiocarboxamide) to thermally revert to the starting materials and/or rearrange to the desired product.
Example 1 - Preparation o~ N-(2-mercaptoethyl)acetamide A l-liter Parr pressure reactor was charged with 192.2 g of anhydrous methanol and hydrogen sulfide (73.0 g;
2.14 moles; 7 percent excess) and the stirred solution heated to 100C. 2-Methyl-2-oxazoline (169.3 g; 1.99 moles) was then pumped into the sealed bomb through a check valve at a rate of approximately 2.5 g/minute. The temperature of the stirred solution rose to 111C during addition and the pressure within the bomb dropped from 320 to 65 psig (22.6-4.59 kg./cm.2). The drop in pressure indicates conversion of H2S to the desired alkanamide. To insure complete conversion, the reactor was heated at this tem-perature for an additional 4 hours. During this post heating period the bomb pressure remained constant indicating the reaction was essentially complete. The reaction mixture was cooled and volatiles removed therefrom under reduced pressure. Analysis of the remaining pot material by standard iodide/iodate titration (mercaptan functional group analysis) indicated 201.9 g of the desired amide, and 85.1 percent yield based on the oxazoline charged.
Distillation under reduced pressure produced a 92.6 percent recovery of a water-white, viscous liquid boiling at 125C/
0.9 mm Hg. Bis(acetamidoethyl)sulfide was produced as a 17.732A-F -5-~L~)8~6 by~product in amounts which essentially accounted for the remainder of the reactants.
N-(2-mercaptoethyl)propionamide was produced in similarly good yields under essentially the same process conditions.
Bxam~e~ Preparation of N-(2-mercaptoethyl)propionamide 2-Ethyl-2-oxazoline (496.4 g; 5.01 moles) was charged to a l-liter stainless steel Parr reactor, equipped with a stirrer, heating means, and a dip tube designed to introduce H2S below the surface of the liquid oxazoline.
The oxazoline was warmed to 70C and hydrogen sulfide (189.5 g, 5.56 moles) was added to the reaction vessel through the dip tube at a rate of 3.7 g per minute. The temperature was maintained at 70-75C during the addition of H2S and for an additional 4.3 hours after the addition was complete. The reaction mixture was subsequently heated at 150C for 5 hours. Aiter this post-heating step, the reaction mixture was cooled to 85C, excess H2S vented to a caustic scrubber, and nitrogen bubbled through the remaining liquid reaction mixture to remove residual ~2S.
Analysis of the clear, brown liquid product (653.7 g) thus obtained indicated that the desired product~ N-(2-mercapto-ethyl)propionamide, was produced in 86.8 percent of theo-retical yield, based on the oxazoline charged. The desired product was recovered from the crude product by use of a falling film still and was thus obtained as a water white liquid containing a minor amount (less than 5 percent) of 2-ethyl-2-thiazoline. The presence of this thiazoline is not a disadvantage since it also hydrolyzes under the conditions set forth below to form the mercaptoethylamine hydrochloride.
17,732A-F -6-'~ . . .
-, .
,.:
s~
Example 3 - Preparation of Mercaptoethylamine Hydrochloride An aliquot o-f the N-(2-mercaptoethyl)acetamide from Example 1 above (119.2 g; 1.00 mole) and 19.5 percent aqueous HCl (205.6 g; 1.10 mole) were combined in a re-action vessel equipped with a magnetic stirrer and reflux condensor. The reaction mixture was heated to reflux (approximately 107C) for 4 hours, under a nitroge~ blanket.
Volatiles were then removed from the reaction mixture under vacuum leaving a viscous, slightly yellow pot liquid which crystallized to a whIte solid upon cooling. The crystalline material (114.0 g) was identified by its nuclear magnetic resonance and infrared spectra as mercaptoethylamine hydrochloride. This salt is an item of commerce having several utilities, especially its use as a pharmaceutical intermediate. This salt can also be neutralized with a base (e.g., NaOH) and used as an epoxy curing agent in epoxy resins. Both the mercapto group and amino group are reactive with the epoxy moiety. See "Handbook of Epoxy Resins" by Lee and Neville, McGraw-Hill Book Company (1967). ~urther, the neutralized salt can be used as an acid scavenger to inhibit acid corrosion. Other mercaptoethylamines can be similarly used.
17,732A-F _7_ ~. .
.. . . .
It has now been discovered that N-t2-mercaptoethyl) alkanamides can be prepared in excellent yield by the present invention, which is a process for preparing an N-(2-mercapto-ethyl)alkanamide comprising reacting under anhydrous con-ditions (a) a 2-H-2-oxazoline or a 2-alkyl-2-oxazoline having the formula ¦ ~C - R
~ ~4 -17,732A-F -1-" ' ' :
1~8~9S6 wherein R is hydrogen or an alkyl group of from 1 to 18 carbon atoms and each of Rl to R4 are hydrogen, lower alkyl, hydroxy-substituted lower alkyl or phenyl, with (b) hydrogen sulfide.
Such products form a known class of useful compounds having many members, all of which can be hydrolyzed with aqueous ~HCl to form a 2-mercaptoethylamine hydrochloride which has utility, when neutralized, as an epoxy curing agent, as an acid scavenger and as a pharma-ceutical intermediate.
The reactants in the instant process are known classes of reactants. The 2-H-a-oxazolineS and 2-alkyl-2--oxazolines correspond to the formula Il :
¦ C - R
~.. .
in which R is hydrogen or an alkyl group of from 1 to 18 carbon atoms, and preferably R is methyl or ethyl. Each of Rl to R4 is hydrogen, lower alkyl (from 1 to 6 carbon atoms), hydroxy-substituted lower alkyl or phenyl. Pref-erably, Rl and R2 are hydrogen, methyl, ethyl or hydroxy-methyl and R3 and R4 are each hydrogen. Most preferably, Rl to R4 are each hydrogen.
Examples of suitable such 2-alkyl~2-oxazoline reactants include those of -formula I having the values of R and Rl to R4 set forth in Table I.
17,732A-F -2-.. .
- ~ . . : . . ' : ,' .: : , . ' : :, . :, . : .
r `~ lV~ 5~;
TABLE I
R Rl R2 R3 R~
H H H H H
C7H15 H ~ H H
CllH23 H H H H
C5HllC6H5 H H C6H5 C2H5 C~Hg ~ H C6H5 The 2-oxazolines used herein are normally prepared by reacting an alkanoic acid with an ethanolamine to form the corresponding acid/amine salt or amide, which in turn is heated in the presence of an aluminum oxide catalyst to form the corresponding 2-alkyl-2-oxazoline product.
The reaction may be conducted neat or in an organic solvent that is inert in the instant process.
Suitable such solvents include the lower alkanols and particularly methanol and combinations of such lower alkanols with conventional hydrocarbon solvents (e.g.
benzene, toluene, etc.). It is preferred to conduct the instant process neat or in methanol. It is also preferred to conduct the reaction under substantially anhydrous conditions. The 2-oxazolines are susceptible to hydrolysis 17,732~-F -3-by water and essentially anhydrous conditions are therefore required to optimize product yield.
The stoichiometry of the reaction requires 1 mole of hydrogen sulfide per mole of 2-alkyl-2--oxazoline reactant. More or less than the stoichio-metric amount of either reactant can be used. However, it is preferred to use an excess of hydrogen sulfide to effect $he completion of the reaction and to maximize the product yield at the expense of by-products, such as bis(alkanamidoethyl) sulfide.
The order of addition or method of blending the reactants is not critical. From a procedural standpoint, however, it is advantageous to add the hydrogen sulfide incrementally to a reaction vessel precharged with the -~
oxazoline reactant, mainly for effectively controlling the reaction temperature.
Substantially any reaction temperature of from about 20 to about 200C can be used but we normally prefer to conduct the reaction at a temperature of from about 50 to about 150C. At these temperatures, the reaction may be conducted under autogenous or superatmospheric pressures in conventional pressure equipment. The instant reaction is e~othermic and normally will not require additional heat after ~he reaction is star~ed. Normally, it is advantageous to conduct the reaction in equipment where the temperature can be controlled by cooling.
It has been observed that the reaction rate and product yields are lower when a reaction temperature in lower ranges are used (e.g. from about 20 to about 70).
17,732A~F _4_ .. ~ . ~.
95!6i In these instances the product yields can be increased by warming the reaction mixture to the preferred tem-perature range (e.g. 100-150C). This post-heating step appears to cause at least one of the by-products (e.g. a hydroxyethyl thiocarboxamide) to thermally revert to the starting materials and/or rearrange to the desired product.
Example 1 - Preparation o~ N-(2-mercaptoethyl)acetamide A l-liter Parr pressure reactor was charged with 192.2 g of anhydrous methanol and hydrogen sulfide (73.0 g;
2.14 moles; 7 percent excess) and the stirred solution heated to 100C. 2-Methyl-2-oxazoline (169.3 g; 1.99 moles) was then pumped into the sealed bomb through a check valve at a rate of approximately 2.5 g/minute. The temperature of the stirred solution rose to 111C during addition and the pressure within the bomb dropped from 320 to 65 psig (22.6-4.59 kg./cm.2). The drop in pressure indicates conversion of H2S to the desired alkanamide. To insure complete conversion, the reactor was heated at this tem-perature for an additional 4 hours. During this post heating period the bomb pressure remained constant indicating the reaction was essentially complete. The reaction mixture was cooled and volatiles removed therefrom under reduced pressure. Analysis of the remaining pot material by standard iodide/iodate titration (mercaptan functional group analysis) indicated 201.9 g of the desired amide, and 85.1 percent yield based on the oxazoline charged.
Distillation under reduced pressure produced a 92.6 percent recovery of a water-white, viscous liquid boiling at 125C/
0.9 mm Hg. Bis(acetamidoethyl)sulfide was produced as a 17.732A-F -5-~L~)8~6 by~product in amounts which essentially accounted for the remainder of the reactants.
N-(2-mercaptoethyl)propionamide was produced in similarly good yields under essentially the same process conditions.
Bxam~e~ Preparation of N-(2-mercaptoethyl)propionamide 2-Ethyl-2-oxazoline (496.4 g; 5.01 moles) was charged to a l-liter stainless steel Parr reactor, equipped with a stirrer, heating means, and a dip tube designed to introduce H2S below the surface of the liquid oxazoline.
The oxazoline was warmed to 70C and hydrogen sulfide (189.5 g, 5.56 moles) was added to the reaction vessel through the dip tube at a rate of 3.7 g per minute. The temperature was maintained at 70-75C during the addition of H2S and for an additional 4.3 hours after the addition was complete. The reaction mixture was subsequently heated at 150C for 5 hours. Aiter this post-heating step, the reaction mixture was cooled to 85C, excess H2S vented to a caustic scrubber, and nitrogen bubbled through the remaining liquid reaction mixture to remove residual ~2S.
Analysis of the clear, brown liquid product (653.7 g) thus obtained indicated that the desired product~ N-(2-mercapto-ethyl)propionamide, was produced in 86.8 percent of theo-retical yield, based on the oxazoline charged. The desired product was recovered from the crude product by use of a falling film still and was thus obtained as a water white liquid containing a minor amount (less than 5 percent) of 2-ethyl-2-thiazoline. The presence of this thiazoline is not a disadvantage since it also hydrolyzes under the conditions set forth below to form the mercaptoethylamine hydrochloride.
17,732A-F -6-'~ . . .
-, .
,.:
s~
Example 3 - Preparation of Mercaptoethylamine Hydrochloride An aliquot o-f the N-(2-mercaptoethyl)acetamide from Example 1 above (119.2 g; 1.00 mole) and 19.5 percent aqueous HCl (205.6 g; 1.10 mole) were combined in a re-action vessel equipped with a magnetic stirrer and reflux condensor. The reaction mixture was heated to reflux (approximately 107C) for 4 hours, under a nitroge~ blanket.
Volatiles were then removed from the reaction mixture under vacuum leaving a viscous, slightly yellow pot liquid which crystallized to a whIte solid upon cooling. The crystalline material (114.0 g) was identified by its nuclear magnetic resonance and infrared spectra as mercaptoethylamine hydrochloride. This salt is an item of commerce having several utilities, especially its use as a pharmaceutical intermediate. This salt can also be neutralized with a base (e.g., NaOH) and used as an epoxy curing agent in epoxy resins. Both the mercapto group and amino group are reactive with the epoxy moiety. See "Handbook of Epoxy Resins" by Lee and Neville, McGraw-Hill Book Company (1967). ~urther, the neutralized salt can be used as an acid scavenger to inhibit acid corrosion. Other mercaptoethylamines can be similarly used.
17,732A-F _7_ ~. .
.. . . .
Claims (11)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for preparing an N-(2-mercaptoethyl) alkanamide comprising reacting under anhydrous conditions (a) a 2-H-2-oxazoline or a 2-alkyl-2-oxazoline having the formula wherein R is hydrogen or an alkyl group of from 1 to 18 carbon atoms and each of R1 to R2 are hydrogenl lower alkyl, hydroxy-substituted lower alkyl or phenyl, with (b) hydrogen sulfide.
2. The process of Claim 1 wherein the process is conducted in an inert organic solvent.
3. The process of Claim 3 wherein the solvent is a lower alkanol of from 1 to 4 carbon atoms.
4. The process of Claim 3 wherein the organic solvent is methanol.
5. The process of Claim 1 wherein the process is conducted neat.
6. The process of Claim 1 wherein R1 and R2 are hydrogen, methyl, ethyl or hydroxymethyl and R3 and R4 are each hydrogen.
7. The process of Claim 6 wherein R1 to are each hydrogen and R is methyl or ethyl.
8. The process of Claim 1 wherein the reaction is conducted at a temperature of from 20° to 200°C.
9. The process of Claim 8 wherein the reaction temperature is from 50° to 150°C.
10. The process of Claim 1 wherein the process is conducted neat under autogenous or superatmospheric pressure.
11. The process of Claim 1 and including the additional step of hydrolyzing the N-(2-mercaptoethyl) alkanamide with aqueous hydrochloric acid to thereby form 2-mercaptoethylamine hydrochloride.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA298,231A CA1088956A (en) | 1978-03-06 | 1978-03-06 | N-(2-mercaptoethyl)alkanamides from h 1n2 xxs and 2-h- 2-oxazolines or 2-alkyl-2-oxazolines |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA298,231A CA1088956A (en) | 1978-03-06 | 1978-03-06 | N-(2-mercaptoethyl)alkanamides from h 1n2 xxs and 2-h- 2-oxazolines or 2-alkyl-2-oxazolines |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1088956A true CA1088956A (en) | 1980-11-04 |
Family
ID=4110913
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA298,231A Expired CA1088956A (en) | 1978-03-06 | 1978-03-06 | N-(2-mercaptoethyl)alkanamides from h 1n2 xxs and 2-h- 2-oxazolines or 2-alkyl-2-oxazolines |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1088956A (en) |
-
1978
- 1978-03-06 CA CA298,231A patent/CA1088956A/en not_active Expired
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