PurposeThe purpose of this paper is to study the effect of new heterocyclic compounds on styrene butadiene rubber (SBR) mixes.Design/methodology/approachIt has been found that the starting material 1 could react with cyromazine (2) and/or 4‐aminoantipyriene (4) as amino compounds in the presence of triethylorthoformate and in the boiling dioxane to yield triazine‐3 and/or pyrazolo 5 derivatives, respectively. The chemical structures of the new products 3 and 5 have been established by their elemental analyses spectroscopic data IR, Ms and 1H, 13C NMR. These two compounds were evaluated as antioxidants in SBR, and this evaluation was confirmed by physico‐mechanical properties of vulcanizates, IR spectra and scanning electron microscope.FindingsThe difference between maximum torque MH and minimum torque ML (ΔM), tensile strength, modulus and elongation at break increases in the presence of prepared antioxidants while the equilibrium swelling decreased. The rubber vulcanizates were subjected to thermal oxidative aging at 90°C for up to seven days. It has been found that new compounds 3 and 5 can protect SBR vulcanizates against oxidative deterioration.Research limitations/implicationsThe solubility of the prepared compounds 3 and 5 is very poor and they are only soluble in dimethyl formamide (DMF) or dimethyl sulphoxide (DMSO) which have high boiling points. Also, new compounds 3 and 5 have melting points (above 300°C).Practical implicationsTriazine and antipyrine derivatives have many medical and industrial applications.Originality/valueThe new synthesized compounds revealed excellent antioxidant behaviour in comparison with the commercial antioxidant phenyl‐β‐naphthyl amine (PβN) which is used in industry.
Syntheses of the title ring systems are described starting with benzothiazol‐2‐ylacetohydrazide (1). Thus, 1 was reacted with carbon disulfide to afford the 2‐methyl heteroaryl derivative 2, which on reaction with hydrazine hydrate yielded the corresponding triazole compound 3. Also, 1 can undergo a reaction with an isothiocyanate to give the N‐thiocarbonyl adduct 4 that can then be cyclized to produce a 2‐methyl heteroaryl analog 5 or 6. Compounds 8 or 9 could be obtained by the reaction of 1 with an aryl aldehyde followed by malononitrile or via its self‐cyclization, respectively. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 177–182, 1999
A series of pyrido[2,3‐d]pyrimidine‐2‐thione derivatives (5a‐c) were synthesized by the one‐pot reaction of the appropriate aldehyde, malononitrile and 6‐aminothiouracil (1) in dimethyl‐formamide. The same compounds were also synthesized by the reaction of arylidine malononitrile (4) with 6‐aminothiouracil (1). Moreover, the chemical behaviour of the produced pyrimidines towards different reagents was studied.
PurposeEvaluation of uracil and/or benzothiazol derivatives as antioxidants in natural rubber mixes.Design/methodology/approachCyanoacetylurea 1, as a precursor, was prepared at a good yield from widely available, low‐cost chemicals. Compound 1 was treated with triethylorthoformate and amine derivatives in one pot reaction affording the target uracil derivative 3. Replacement of the cyano group in 1 by benzothiazol led to obtaining the interesting N‐hydroxy uracils containing benzothiazole moiety 5 at a good yield. Some of the compounds prepared was selected and were evaluated as antioxidants in natural rubber mixes. The rheometric characteristic of the compounded rubber and the physico‐mechanical properties of the vulcanizates were determined.FindingsThe cure rate index, tensile strength and modulus increased while the equilibrium swelling decreased, i.e. compound 5 behaved as a secondary accelerator. The rubber vulcanizates were subjected to thermal oxidative ageing at 90°C for up to seven days. It has been found that uracil and/or benzothiazol derivatives can protect natural rubber vulcanizates against oxidative deterioration.Research limitations/implicationsThe compounds prepareds were difficult to dissolve, they needed solvents with high boiling points, e.g. DMF, DMSO to be dissolved and even then they are not completely dissolved.Practical implicationsUracil and or benzothiazol derivatives have many industrial applications.Originality/valueThe new compounds were prepared from very cheap and widely available chemicals. The compounds synthesised showed good antioxidant behaviour in comparison with the commercial antioxidant (phenyl‐β‐naphthyl amine) industrially used.
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