Chemical changes in rubber allergens during vulcanization

Allergic contact dermatitis to rubber is caused by residues of chemicals used in manufacturing a rubber product. Several different additives are used to achieve a final product of the desired characteristics. Accelerators such as thiurams, dithiocarbamates, and mercaptobenzothiazoles are often among the additives responsible for allergic reactions recognized by dermatologists. The chemistry of the vulcanization process is complicated; as it occurs at an elevated temperature with a mixture of reactive chemicals, the compositions of the initial and final products differ. This paper investigates the changes in composition of common allergens during vulcanization, doing so by chemically analysing various rubber formulations at different stages of the process. Major changes were found in which added chemicals were consumed and new ones produced. An important observation is that thiuram disulfides rarely appear in the final rubber although they may have been used as additives. Instead, thiurams are often converted to dithiocarbamates or to products formed by addition to mercaptobenzothiazole structures, if these have been used together with thiurams as accelerators.

Contact dermatitis to a rubber allergen with both dithiocarbamate and benzothiazole structure

Contact dermatitis to rubber products are often caused by additives used during manufacture, and diagnosed from patch test with established rubber allergen series. In these series the compounds are divided into separate groups such as thiurams, dithiocarbamates and mercaptobenzothiazoles. The objectives were to investigate the substances with allergenic structures present in a diving mask giving rise to facial dermatitis, also those substances including structures from different groups of rubber chemicals. The rubber material was analysed by high-performance liquid chromatography and diode-array detector. The patient was tested by epicutaneous tests using pure substances, extracts and authentic rubber material. 2-Benzothiazolyl-N,N-diethylthiocarbamylsulfide, was found in the diving mask and the patient showed positive reaction to the pure compound and to extracts of the diving mask. This compound has structures of both mercaptobenzothiazole and thiuram/dithiocarbamate in its formulae. Besides the established groups of rubber accelerators, uncommon allergens with structures from more than one group can be formed or added at vulcanization. Chemical analysis of the product is needed to find these allergens.

High-performance liquid chromatography analysis of rubber allergens in protective gloves used in health care

A high-performance liquid chromatography (HPLC) method developed for analysis of zinc dithiocarbamates was validated and used to perform a survey of disposable medical gloves used in southern Sweden. The gloves were extracted with acetone at room temperature for 10 min by shaking. The extracts were injected into a polyether ether ketone lined HPLC column, and peaks were analysed by a diode-array detector. The survey shows that of 19 gloves analysed, 10 contained zinc diethyldithiocarbamate (0.070-3.5 mg/g), 3 contained zinc pentamethylenedithiocarbamate (1.0-4.3 mg/g), 4 contained zinc dibutyldithiocarbamate (0.9-1.1 mg/g), and 2 contained 2-mercaptobenzothiazole (0.005-0.008 mg/g). None of them contained thiurams.

Extraction of haptens from solid products and their delivery to the skin, exemplified by dithiocarbamates from rubber gloves

Allergic contact dermatitis is often caused by solid products such as rubber gloves. Patch testing with the product as is often gives negative results. Extraction of the haptens into an organic solvent is commonly performed to achieve a more correct investigation. The technique used for extraction of haptens from solid materials is only sporadically described. In this study, we investigated and optimized the yields of dithiocarbamates obtained by extraction from rubber gloves. The influence of solvent, extraction time and the procedures for extraction are evaluated. The delivery of zinc dibutyldithiocarbamate from the patch test preparation to the skin is determined.

HPLC analysis of alkyl thioureas in an orthopaedic brace and patch testing with pure ethylbutylthiourea

Ethylbutylthiourea (EBTU) is an accelerator used in the production of chloroprene (neoprene) rubber. EBTU occurs in a mixture with diethylthiourea (DETU) and dibutylthiourea (DBTU) in the accelerator. An analytical method originally developed for analysis of zinc dithiocarbamates in rubber has been used to analyse EBTU, DETU and DBTU in a knee brace responsible for an allergic contact dermatitis in a gardener suffering from arthrosis. EBTU was isolated and gave positive reactions when tested as a pure compound. The test reaction was accompanied by positive reactions to DETU and DBTU.

Spontaneous formation of thiuram disulfides in solutions of iron(III) dithiocarbamates

Dithiocarbamates are used as pesticides and rubber additives. Dithiocarbamates are the reduced forms of thiuram disulfides and both of these groups of substances induce allergic contact dermatitis. The allergic cross-reactivity pattern between dithiocarbamates and thiurams is unclear. The aim of this study was to investigate why these cross-reactions occur sometimes but not always. HPLC-analysis of buffer solutions of iron(III) dithiocarbamates demonstrated that thiuram disulfides were formed spontaneously and rapidly in high yield. No such oxidation was observed in solutions of copper(II), zinc(II), or sodium dithiocarbamates. However, sodium diethyldithiocarbamate and zinc diethyldithiocarbamate were oxidized in buffer solution when ferric salt was added. The influence of different metal ions on the oxidation reaction is probably an explanation for the cross-reactivity patterns seen between dithiocarbamates and thiurams. These findings also show that careful handling is necessary in analytical and biological studies with solutions of iron(III) dithiocarbamates. Oxidation of dithiocarbamates in aqueous buffer at physiological pH has not been shown before.

Stability of thiuram disulfides in patch test preparations and formation of asymmetric disulfides

The thiuram mix used in patch testing originally contains 4 compounds. However, chemical analysis of the test preparation revealed that several new compounds are spontaneously formed during storage. The structures of these compounds have been determined and the rate of their formation has been studied in buffer solution at pH 7.4. After a few hours, a large amount of mixed disulfides are formed in solutions originally containing only symmetric disulfides. The impact on the test result of the formation of asymmetric disulfides has been investigated by testing on thiuram-sensitive volunteers with different preparations of mixed thiuram disulfides. In our study, the formation of new asymmetric thiuram disulfides from the original symmetric thiuram disulfides in the test preparation had no influence on the result of the patch testing. However, as the chemical analysis showed that the mix composition changes during the period when the preparations are used, and differs between suppliers, the question is raised as to whether it is acceptable to use test preparations with a composition that is different from that labelled on the protocol.

Activation and cross-reactivity pattern of a new allergen in adhesive plaster

N,N'-disalicylidene-1,2-diaminopropane is a copper inhibitor present in some adhesive plasters, rubber products and gasoline. Upon contact with water it is hydrolyzed to salicylaldehyde and 1,2-diaminopropane. All patients in this study showed positive patch-test reactions to N,N'-disalicylidene-1,2-diaminopropane, and also to 1,2-diaminopropane and ethylenediamine. None reacted to salicylaldehyde. Patch testing with different N,N'-disalicylidene-derivatives showed localization of the amino groups in positions 1 and 2 to be a prerequisite of cross-reactivity to 1,2-diaminopropane and ethylenediamine. An extraction procedure and a high-performance liquid chromatography (HPLC) method for the analysis of adhesive plasters is described. Studies of the hydrolysis of the copper inhibitor at physiological pH showed rapid formation of 1,2-diaminopropane under biomimetic conditions.