GB1599357A

GB1599357A - N,n'-(thiocarbonyl)thio)dimorpholine and benzothiazole sulphenamides useful as rubber accelerators

Info

Publication number: GB1599357A
Application number: GB25188/78A
Authority: GB
Original assignee: American Cyanamid Co
Current assignee: Wyeth Holdings LLC
Priority date: 1977-07-11
Filing date: 1978-05-31
Publication date: 1981-09-30
Also published as: AR219326A1; BR7804438A; DE2827933A1; FR2397435A1; AU3658378A; JPS5419975A; PL208317A1; DD137236A5; CA1105918A; SE7807701L

Description

(54) STABILIZED N,N'-[(THIOCARBONYL)THIO] DIMORPHOLINE AND BENZOTHIAZOLE SULFENAMIDES USEFUL AS RUBBER ACCELERATORS (71) We, AMERICAN CYANAMID COMPANY, a corporation organised and existing under the laws of the state of Maine, United States of America, of Berdan Avenue, Township of Wayne, State of New Jersey, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to stabilized N,N'.- [(thiocarbonyl)thio]dimorpholine and benzothiazole sulfenamides which are useful as rubber stabilizers.

N,N' - [(thiocarbonyl)thioidimorpholine and 2 - benzothiazole sulfenamide are rubber accelerators which are widely used in the rubber industry. While the compounds are readily prepared according to well-known procedures in a high state of purity, they deteriorate when exposed to elevated temperatures and/or humid conditions. The deterioration of the sulfenamides is manifested by a gradual build-up of mercaptobenzothiazyl disulfide (MBTS) resulting in an alteration of the cure characteristics normally exhibited by the accelerator when used in a rubber vulcanizate. Since elevated temperatures and humid conditions are common in the summer months and throughout the warmer areas of the world, it is desirable to find a means for either stopping or retarding this deterioration without destroying the accelerating activity of the compounds.

It has now been found that the incorporation of a minor amount of an oxirane (epoxy) compound into the N,N' - [(thiocarbonyl)thio]dimorpholine and the benzothiazole sulfenamides significantly reduces the deterioration of the accelerators on exposure to temperature and/or humidity.

2 - Benzothiazole sulfenamides accelerators to which this invention relates may be represented by the general formula:

wherein R and R' individually represent hydrogen, alkyl of 1 to 8 carbon atoms, inclusive, cycloalkyl of 5 to 6 carbon atoms, inclusive, or, taken together with the nitrogen atom, combine to form a heterocyclic ring, and n is 0 or 1.They are readily prepared by well-known procedures, see for example, United States Patent Nos. 2,730,526: 2,730,527; 2,758,995; 2,776,297; 2,840,556: 2,981,325; 3,055,909; 3,161,648: and 3658,808. Some of the more commonly used accelerators include N- isopropyl - 2- benzothiazole sulfenamide; N,N- diisopropyl - 2benzothiazole sulfenamide; N - t - butyl - 2 - benzothiazole sulfenamide; N cyclohexyl- 2- benzothiazole sulfenamide; N,N - dicyclohexyl- 2benzothiazole sulfenamide; N - oxydiethylene - 2 - benzothiazole sulfenamide; 4 - morpholinyl - 2 - benzothiazole disulfide; N - t - octyl - 2 - benzothiazole sulfenamide; N,N- dicyclopentyl- 2- benzothiazole sulfenamide; N,Ndiethyl - 2 - benzothiazole sulfenamide; and N - methyl - 2 - benzothiazole sulfenamide.

N,N' - [(thiocarbonyl)thio]dimorpholine is an old compound. It can be readily made by reacting sodium 4- morpholinocarbodithioate (II) with Nchloromorpholine (III):

Another method is described whereby (II) is reacted with morpholine and an oxidizing agent such as an aqueous solution of iodine and potassium iodide or sodium hypochlorite or other oxidizing agent known in the art for the preparation of thiocarbonylsulfides.

Use of the compound as an accelerator is described by Taylor, Rubber Chem.

& Tech. 47 (No. 4), 906-910 (1974).

The oxirane compounds which are useful herein are those solid or liquid organic oxirane compounds having a molecular weight of greater than 60 and have no functional groups reactive with the dimorpholine and sulfenamide other than the oxirane ring. These compounds include, but are not limited to, alkyl, cycloalkyl and aryl glycidyl ethers; mono- and diepoxidized alkenes and dienes, including epoxidized diene polymers, such as 1,2- and 2,3-epoxybutane and epoxidized polybutadiene; cycloalkylene oxides such as cyclohexene oxide and vinyl cyclohexene diepoxide; diglycidyl ethers of aliphatic diols such as the diglycidyl ether of 1,4-butanediol; diglycidyl ethers of bisphenols such as the diglycidyl ether of isopropylidene bisphenol (Bisphenol A) or diglycidyl ethers of methylene bisphenol and oligomers thereof; epoxidized oils such as epoxidized linseed oil; epoxidized unsaturated diglycidyl ethers of polymeric diols; and polyglycidyl ethers of polyols.

In practicing the invention, the N,N'-[(thiocarbonyl)thio]dimorpholine or the sulfenamide is blended in any convenient manner consistent with the invention with the oxirane compound. Since N,N'[(thiocarbonyl)thioldimorpholine is not very stable, the procedure used to blend it with the oxirane should avoid exposure to elevated temperatures for too long a period of time. Nevertheless, one method of producing the blend is to melt the N,N'-[(thiocarbonyl)thio]dimorpholine, blend in the appropriate oxirane compound, allow the molten blend to cool and either flake or grind the resultant solid for use. Alternatively, the oxirane and dimorpholine may be dry blended.The blending method is not critical to the invention; however, it will be understood that not all stabilizer compounds will melt or dissolve into the molten accelerator and dispersions may sometimes result, and that, in some instances, it may be better to dry blend and vice versa.

The sulfenamides are often prepared by cooling and flaking the molten compound. In this case, it is possible to incorporate the oxirane compound into the melt before cooling and flaking.

The blends may be prepared in any weight ratio without incident, but preferably the oxirane concentration should range from 0.1 percent, by weight, to 5.0 percent, by weight, depending on the particular stabilizer, it being realized that the stabilizers may vary in their effectiveness in stabilizing the accelerator compound. More preferably, the dimorpholine or the sulfenamide may be effectively stabilized against deterioration on aging using 0.5 to 3 percent, by weight, of the oxirane compound, based on the weight of the dimorpholine or sulfenamide.

Stabilization, as defined for the purposes of this invention, means any significant improvement in the stability of the N,N' [(thiocarbonyl)thio]dimorpholine or the sulfenamide after storing for a period of time at normal room temperature or at an elevated temperature. An accelerated aging test which exemplifies the stabilization of the dimorpholine is defined hereinbelow. Improvement in stability means any significant reduction of the loss of cure rate experienced by use of the unstabilized dimorpholine during a similar period of storage under the same conditions, and/or any significant decrease in the loss of scorch protection (scorch time) relative to the unstabilized dimorpholine.

The unstabilized compound ordinarily suffers degradation on storage over a period of time such that its use in a vulcanization results in a slower rate of cure and oftentimes a reduction in scorch time. This is often manifested in the vulcanized rubber product by slower development of the optimum modulus properties and in many cases the extent of the full cure may be effected, i.e., the optimum properties may not be attained.

Cure rate is determined by use of a Monsanto Oscillating Disc Rheometer and is reported as the maximum slope of the cure curve in inch-pounds per 0.5 minute operating against an oscillating disc embedded in the rubber stock undergoing vulcanization.

Mooney Scorch Time is the elapsed time from the onset of the heating cycle to the start of vulcanization (induction period). With reference to the cure curve traced by the Mooney Viscometer, scorch is reported as t5, which is the time, in minutes, from one minute after the start of heating, for a five point rise in the cure curve above the minimum in the curve, at the temperature of the test, which is usually chosen to represent maximum processing temperature of the unvulcanized rubber composition.

The stabilized N,N - [(thiocarbonyl)thio]dimorpholine is evaluated, as discussed above, in terms of the improvement over an unstabilized sample thereof after a period of aging. It is difficult to determine what constitutes normal storage conditions, in terms of the physical form of storage (drums, fiber packs, paper bags, etc.), the length of storage in days, weeks or months, or the temperature of storage (air-conditioned warehouses or exposure to ambient temperature in the warmer climates). In order to evaluate the effectiveness of the stabilizers by a reasonable set of conditions, unless otherwise stated, the stabilized and unstabilized compounds were stored in closed containers fbr (a) two weeks at normal room temperature (25--30"C.), (b) for one month at 450C., and (c) two months at 450C.

The compounds were then evaluated in a standard rubber formulation as described in the following illustrative examples.

In the examples which follow, the compounds were evaluated for effectiveness of the stabilizer using the rubber masterbatch shown below (which contains 100 parts by weight of rubber stock): Masterbatch Styrene-butadiene rubber (oil-extended) 89.5 Cis-4 Polybutadiene 35.0 Aromatic oil 25.5 Carbon black 75.0 Zinc oxide 5.0 Stearic acid 1.5 N-Phenyl-N'-(1 3-dimethylbutyl) p-phenylenediamine 1.0 Sulfur 1.8 Example 1 To a sample, comprising 100 parts of N,N - [(thiocarbonyl)thio]dimorpholine, are added 4.0 parts of 3,4 - epoxycyclohexylmethyl - 3,4 - epoxycyclohexane carboxylate.

The stabilized sample is then added to the above masterbatch after storage for 6 weeks at 25% RH and 45"C., at a concentration of 0.9 part of stabilized sample to 100 parts of masterbatch, as described above, with compounding.

The sample is then subjected to testing in order to ascertain the accelerator activity in promoting the vulcanization reaction as measured by the cure rate and is identified as Composition A. A sample containing no stabilizer is set forth for comparative purposes, in Table I, below.

TABLE I None A Maximum Cure Rate Oscillating Disc Rheometer&commat; 316"F.

(in.-lbs.A).5 min) 6 Weeks 3.4 3.8 Maximum Torque (inch-pounds) 6 Weeks 44.5 49.5 Scorch Time (t5) (minutes) Mooney Viscometer &commat; 270"F.

6 Weeks 12.8 24.0 The data show that N,N' - [(thiocarbonyl)thio]dimorpholine is improved (stabilized against degradation) by the incorporation therein of 4.0 percent, by weight, of the epoxy compound, as shown by the retention of cure rate after storage for 6 weeks at 450 C. and 25% RH and by the stability of the Mooney Scorch.

Examples 2-5 The procedure of Example 1 is again followed except that the oxiranes are (B) 2.0% of epoxidized soybean oil, (C) 1.0% of vinyl cyclohexene diepoxide, (D) 5.0 ', of the diglycidyl ether of 1 4-butanediol, and (E) 0.75% of the diglycidyl ether of 4,4' - isopropylidenebisphenol. In each instance, effective stabilization of the N,N - [(thiocarbonyl)thio]dimorpholine is accomplished.

Example 6 Again, following the procedure of Example 1, except that the oxirane comprises 2.5% of the diglycidyl ether of phenol-formaldehyde condensate, satisfactory stabilization is achieved.

Example 7-10 When the stabilizer of Example 1 is replaced by (F) 0.5% of 2,3 epoxypropyl - n - hexylether, (G) 1.0% of epoxidized butyl linseed oil, (H) 3.5 Ó of epoxidized linseed oil, and (I), 4.0% of 2,2 - bis[4 - (2,3 epoxypropoxy)phenyl]propane; effective stabilization of the accelerator is achieved.

Example 11 Stabilization of N-isopropyl-2-benzothiazole Sulfenamide Samples of N - isoprooyl - 2 - benzothiazole sulfenamide are mixed with 20 of (J) 2,3 - epoxypropyl- n- hexyl ether and (K) 2,2 - bis[4 - (2,3 epoxypropoxy)p enylipropane. The samples are then exposed for periods of 2 weeks and 4 weeks at normal room temperature and 75 zÓ humidity and then analyzed for build-up of mercaptobenzothiazyldisulfide (MBTS). The results are shown below in Table II.

TABLE II %MBTS Ó Assay Loss 2 Weeks 4 Weeks 4 Weeks Example Initial &commat; 75 /O RH &commat; 75% RH &commat; 75% RH Control 0.002 0.54 1.73 6.1 llJ 0.001 0.02 0.58 11K 0.001 0.01 0.22 1.6 The data illustrate the effectiveness of the epoxy compounds in preventing deterioration of the sulfenamide on exposure to humidity, as manifested by buildup on MBTS.

Example 12 Samples of N - isopropyl - 2 - benzothiazole sulfenamide are mixed with 2 ó of (L) 3,4 - epoxycyclohexyl methyl - 3,4 - epoxycyclohexane carboxylate, and (M) epoxidized butyl linseed oil. The samples are then exposed for periods of 2 weeks at 75% RH and 2 weeks at 450C./25% RH and then analyzed for build-up of MBTS.

Results are shown below in Table III.

TABLE III MBTS 2 Weeks 2 Weeks at Example Initial &commat; 75% RH 45 C./25% RH Control 0.002 0.26 1.01 12L 0.002 0.008 0.01 12M 0.001 0.09 0.43 Example 13 A sample of N - isopropyl - 2 - benzothiazole sulfenamide is mixed with 2% of (N) epoxidized linseed oil and the sample is exposed for periods of 2 weeks at 450C.

and 4 weeks at 75% RH. The sample is then analyzed for build-up of MBTS.

The results are set forth in Table IV, below.

TABLE IV MBTS % Assay Loss 2 Weeks 2 Weeks 5 Weeks Example Initial &commat; 45"C. &commat; 75% RH &commat; 45"C.

Control 0.003 0.21 1.7 2.8 13N 0.002 0.006 0.02 1.3 Example 14.

Stabilization of N,N-Diisopropyl-2-benzothiazole Sulfenamide A sample of N,N - diisopropyl - 2 - benzothiazole sulfenamide is mixed with 2% of (P) epoxidized linseed oil and then exposed for 10 weeks at 450C./25% RH.

The sample is then analyzed for MBTS build-up.

The results are set forth in Table V, below.

TABLE V ",', MBTS 10 Weeks Example Initial 45 C./25% RH % Assay Loss Control 0.00 0.22 2.3 14P 0.00 0.00 0.9 Example 15 The following sulfenamides are mixed with epoxide (L), as shown in Table VI, and then exposed for periods of one week and 2 weeks at 450C./25% RH. The samples are then analyzed for MBTS build-up.

I. N-tert.butyl-2-benzothiazole sulfenamide

II. N-oxydiethylene-w-benzothiazole sulfenamide

III. N-cyclohexyl-2-benzothiazole sulfenamide

TABLE VI % MBTS Example Initial 1 Week 2 Weeks 5 Weeks 15-I 0.003 1.02 - 15-I+1% L 0.004 0.18 - 15-II 0.002 0.008 0.12 3.94 15-II+3% L 0.002 0.004 0.02 0.02 15-III 0.004 0.56 1.62 15-III+1% L 0.01 0.06 0.06 Examples 1621 The procedure of Example 14P is again followed except that the epoxy compound, in each instance, is replaced by:: 16. 3% of vinylcyclohexene diepoxide 17. 1.5% of styrene oxide 18. 2.0% of the diglycidyl ether of 1,4-butanediol 19. 1.0% of the diglycidyl ether of 4,4'-isopropylidenebisphenol 20. 2.0% of the glycidyl ether of phenol-formaldehyde condensate 21. 3.0% of expoxidized soybean oil In each instance, a substantially equivalent reduction in MBTS build-up is observed.

Examples 22-29 The procedure of Example 11K is again followed except that the N isopropyl - 2 - benzothiazole sulfenamide is replaced by: 22. 4-morpholinyl-2-benzothiazole disulfide 23. N,N-dicyclohexyl-2-benzothiazole sulfenamide 24. N-t-octyl-2-benzothiazole sulfenamide 25. N,N-dicyclopentyl-2-benzothiazole sulfenamide 26. N-methyl-2-benzothiazole sulfenamide 27. N-isopropyl-2-benzothiazole disulfide 28. N,N-diisopropyl-2-benzothiazole disulfide 29. N,N-diethyl-2-benzothiazole sulfenamide.

In each instance, the 2,2-bis[4-(2,3-epoxypropoxy)phenyllpropane effectively prevented deterioration of the compounds.

WHAT WE CLAIM IS: 1. - A stabilized accelerator composition for rubber, comprising (1) a benzothiazole sulfenamide having the formula:

wherein R and R' are, individually, alkyl of 1--8 carbon atoms, inclusive, cycloalkyl of 5--6 carbon atoms, inclusive, or, taken with the nitrogen, combine to form a heterocyclic ring, and n is 0 or 1 and (2) an effective stabilizing amount of an oxirane compound having a molecular weight greater than 60.

2. A composition according to Claim 1, wherein (1) is N - isopropyl - 2 benzothiazole sulfenamide.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

III. N-cyclohexyl-2-benzothiazole sulfenamide

TABLE VI % MBTS Example Initial 1 Week 2 Weeks 5 Weeks

15-I 0.003 1.02 - 15-I+1% L 0.004 0.18 - 15-II 0.002 0.008 0.12 3.94 15-II+3% L 0.002 0.004 0.02 0.02 15-III 0.004 0.56 1.62 15-III+1% L 0.01 0.06 0.06 Examples 1621 The procedure of Example 14P is again followed except that the epoxy compound, in each instance, is replaced by:: 16. 3% of vinylcyclohexene diepoxide 17. 1.5% of styrene oxide 18. 2.0% of the diglycidyl ether of 1,4-butanediol 19. 1.0% of the diglycidyl ether of 4,4'-isopropylidenebisphenol 20. 2.0% of the glycidyl ether of phenol-formaldehyde condensate 21. 3.0% of expoxidized soybean oil In each instance, a substantially equivalent reduction in MBTS build-up is observed.

Examples 22-29 The procedure of Example 11K is again followed except that the N isopropyl - 2 - benzothiazole sulfenamide is replaced by: 22. 4-morpholinyl-2-benzothiazole disulfide 23. N,N-dicyclohexyl-2-benzothiazole sulfenamide 24. N-t-octyl-2-benzothiazole sulfenamide 25. N,N-dicyclopentyl-2-benzothiazole sulfenamide 26. N-methyl-2-benzothiazole sulfenamide 27. N-isopropyl-2-benzothiazole disulfide 28. N,N-diisopropyl-2-benzothiazole disulfide 29. N,N-diethyl-2-benzothiazole sulfenamide.

In each instance, the 2,2-bis[4-(2,3-epoxypropoxy)phenyllpropane effectively prevented deterioration of the compounds.

WHAT WE CLAIM IS: 1. - A stabilized accelerator composition for rubber, comprising (1) a benzothiazole sulfenamide having the formula:

wherein R and R' are, individually, alkyl of 1--8 carbon atoms, inclusive, cycloalkyl of 5--6 carbon atoms, inclusive, or, taken with the nitrogen, combine to form a heterocyclic ring, and n is 0 or 1 and (2) an effective stabilizing amount of an oxirane compound having a molecular weight greater than 60.
2. A composition according to Claim 1, wherein (1) is N - isopropyl - 2 benzothiazole sulfenamide.
3. A composition according to Claim 1, wherein (1) is N,N-diisopropyl-2

benzothiazole sulfenamide.
4. A composition according to Claim I wherein (1) is N-cyclohexyl-2benzothiazole sulfenamide.
5. A composition according to Claim 1, wherein (2) is 2,2 - bis[4 - (2,3 epoxypropoxy)phenyl]propane.
6. A composition according to any preceding claim, wherein (2) is epoxidized linseed oil.
7. A composition according to any one of Claims 1--4, wherein (2) is 3,4 epoxycyclohexylmethyl - 3,4 - epoxycyclohexane carboxylate.
8. A composition according to any one of Claims 1--4, wherein (2) is epoxidized soyabean oil.
9. A composition according to any preceding claim, wherein (2) is present in an amount of from 0.1 to 5.0 percent by weight, based on the weight of (1).
10. A stabilized accelerator composition for rubber, comprising (1) N,N' [(thiocarbonyl)thio]dimorpholine and (2) an effective stabilizing amount of an oxirane compound having a molecular weight greater than 60.
11. A composition according to Claim 10, wherein (2) is as defined in any one of Claims 5-8.
12. A composition according to Claim 10 or Claim 11, wherein (2) is present in an amount of from 0.1 to 5.0 percent by weight, based on the weight of (1).
13. A stabilized accelerator composition, according to Claim 1 and substantially as described in any one of Examples 11-29 herein.
14. A stabilized accelerator composition according to Claim 10 and substantially as described in any one of Examples 1--10 herein.