2-Mercaptobenzothiazole (MBT, CAS 149-30-4): Rubber Accelerator, Intermediate and Uses
2-Mercaptobenzothiazole (MBT) is one of the most important thiazole rubber chemicals and a building block for a whole family of accelerators. It is used directly as a rubber accelerator, as a flotation collector, and as a lubricant additive – but its largest strategic role is as the intermediate from which MBTS, CBS, TBBS and other benzothiazole accelerators are made. This article covers what MBT is, its specification, how it is made, where it is used, and how to specify and buy it.
1. What MBT is
| Property | Value |
|---|---|
| Name | 2-Mercaptobenzothiazole (MBT) |
| CAS number | 149-30-4 |
| Formula / MW | C7H5NS2 / 167.25 g/mol |
| Synonyms | 2-benzothiazolethiol, 2-benzothiazolinethione, MBT |
| Appearance | Off-white to pale-yellow powder or granules |
Chemically it is a benzothiazole ring carrying a thiol (-SH) group, which exists largely in the thione form. That thiol/thione group is what makes MBT both a vulcanisation accelerator and a strong collector for metal sulphides.
2. Specification (typical commercial grade)
| Property | Specification |
|---|---|
| Appearance | Off-white to pale-yellow powder or granules |
| Initial melting point | 170.0 deg C min |
| Loss on heating (100 +/- 2 deg C) | 0.30% max |
| Ash (750 +/- 25 deg C) | 0.30% max |
| Residue on 150 um sieve | 0.10% max |
| Purity (titration / HPLC) | 97.0% min |
Purity and initial melting point are the parameters that most affect accelerator performance; loss on heating controls the moisture that can disturb a rubber compound. Confirm all of them on the batch COA.
3. How MBT is made
The classical industrial route reacts aniline with carbon disulfide and sulfur under pressure at high temperature to close the benzothiazole ring. MBT can also be produced from o-nitrochlorobenzene. Either way, the crude product is purified (for example by dissolution and re-precipitation) to reach the commercial assay, then dried and milled to the required particle size.
4. MBT as a rubber accelerator
MBT is a thiazole accelerator for natural and synthetic rubbers. It gives a fast cure and is classed as a semi-ultra accelerator; it is often used together with a second accelerator to fine-tune scorch safety and cure rate.
| Rubber / system | How MBT is used |
|---|---|
| NR, SBR, BR | Primary or secondary accelerator, usually with a thiuram or guanidine co-accelerator |
| NBR | Accelerator in general-purpose compounds |
| Latex and adhesives | Accelerator in aqueous and solvent-based systems |
| General rubber goods | Footwear, hoses, belting, mechanical goods |
MBT cures quickly but has a relatively short scorch time, which is why it is often combined with a co-accelerator (for example a thiuram or a guanidine) rather than used alone.
5. MBT as an intermediate
A large share of MBT production is not sold as an accelerator at all – it is converted into other benzothiazole accelerators:
| Derivative | Made from MBT by | Character |
|---|---|---|
| MBTS (dibenzothiazyl disulfide) | Oxidative coupling | Slower, safer than MBT; better scorch safety |
| CBS (N-cyclohexyl-2-benzothiazolesulfenamide) | Reaction with cyclohexylamine + oxidant | Delayed-action (sulfenamide) accelerator |
| TBBS (N-tert-butyl-2-benzothiazolesulfenamide) | Reaction with tert-butylamine + oxidant | Delayed-action accelerator; widely used in tyres |
Because of this, MBT demand tracks the whole thiazole accelerator market, not just direct MBT use.
6. MBT in mineral flotation
MBT is also a well-known flotation collector. Its thiol group adsorbs on sulphide minerals, and it is used in sulphide flotation and in the sulphidised flotation of oxide ores (for example oxidised copper minerals). See MBT in mineral flotation for the collector chemistry and practice, and the mining reagents overview for where it fits with xanthates and other collectors.
7. MBT in lubricants and other uses
- Lubricant additive – antioxidant and extreme-pressure component in lubricants and greases.
- Corrosion inhibition – the thiol group bonds to metal surfaces, giving corrosion protection in some systems.
- Industrial biocide – used in some industrial preservative applications.
8. MBT vs MBTS and CBS
| Accelerator | Type | Cure speed | Scorch safety | Typical role |
|---|---|---|---|---|
| MBT | Thiazole (semi-ultra) | Fast | Lower | Primary or co-accelerator; intermediate feedstock |
| MBTS | Thiazole (dibenzothiazyl disulfide) | Moderate | Better than MBT | Where more scorch safety is needed |
| CBS | Sulfenamide (delayed action) | Delayed then fast | High | Tyre and technical compounds needing processing safety |
| TBBS | Sulfenamide (delayed action) | Delayed then fast | High | Tyres and technical rubber goods |
The trade-off is always speed against processing safety: MBT is the fast, low-cost option, while the sulfenamides (CBS, TBBS) delay the onset of cure to give the compound time to be shaped before it sets.
9. Typical dosage
| Use | Typical dosage (starting point) |
|---|---|
| Rubber accelerator | About 0.5 – 2.5 phr (parts per hundred rubber), with a co-accelerator and sulfur per the formulation |
| Flotation collector | Set by ore and circuit tests |
Dosage is formulation-specific. These are starting points for a compound-development programme, not a specification.
10. Safety and regulation
- Skin sensitizer. MBT is classified as a skin sensitizer (H317); repeated skin contact can cause allergic contact dermatitis. Use gloves, avoid dust, and follow the SDS.
- Aquatic toxicity. MBT is toxic to aquatic life; prevent release to water and manage dust and waste properly.
- Dust. Handle as a fine powder with local exhaust ventilation; avoid generating airborne dust.
- Documentation. Confirm the current classification, labelling and transport requirements on the SDS for your market.
11. Packaging, storage and supply
| Item | Detail |
|---|---|
| Packaging | 25 kg PP/PE bags, 1000 kg jumbo bags; palletised for container shipment |
| Storage | Sealed, cool and dry, away from oxidising agents and strong acids |
| Documents | Per-batch COA and SDS; third-party inspection on request |
| Delivery | FOB or CIF to your port; quote by tonnage |
Tell us the application (accelerator or flotation), the tonnage and the delivery port for a quotation.
Frequently Asked Questions
What is MBT used for?
Mainly as a thiazole rubber accelerator and as the intermediate for other benzothiazole accelerators (MBTS, CBS, TBBS). It is also used as a flotation collector and a lubricant additive.
What is the difference between MBT and MBTS?
MBTS is the disulfide made by oxidatively coupling two MBT molecules. MBTS cures more slowly but has better scorch safety than MBT.
Is MBT a primary or secondary accelerator?
It is a fast (semi-ultra) thiazole accelerator, often used as the primary accelerator with a co-accelerator, or as a secondary accelerator with a sulfenamide.
What is the typical dosage of MBT?
About 0.5-2.5 phr in rubber, depending on the formulation and the co-accelerator. Flotation dosage is set by ore testing.
Is MBT hazardous?
Yes – it is a skin sensitizer (H317) and is toxic to aquatic life. Use dust control and PPE and follow the SDS.
Related reading
- MBT in rubber compounding: applications, dosage and co-accelerators
- MBT vs MBTS and CBS: choosing a thiazole rubber accelerator
- MBT in mineral flotation
- How to buy MBT: specs, COA and packing
- Mining reagents overview
- 2-Mercaptobenzothiazole (MBT, CAS 149-30-4) – product page
PolyBlueChem supplies 2-mercaptobenzothiazole (MBT, CAS 149-30-4) with 97% min purity against a full specification, in 25 kg bags and 1000 kg jumbo bags, with per-batch COA and SDS and FOB/CIF delivery. Contact us with your tonnage and delivery port.