Accelerator MBTS (DM, CAS 120-78-5): Properties and Applications

What Is Accelerator MBTS (DM)?

Accelerator MBTS, also called DM, CAS 120-78-5, chemically 2,2′-dibenzothiazyl disulfide, is a thiazole-type rubber accelerator. It is a general-purpose accelerator with good scorch safety, used on its own or as a secondary accelerator (often with DPG) in tyres, technical rubber goods and general rubber.

Thiazole accelerators were the first widely used organic accelerators, and MBTS remains in heavy use because it is effective, versatile and forgiving. It is the disulfide counterpart of MBT: where MBT is the thiazole thiol, MBTS is the disulfide formed by joining two thiazole units through sulfur. That difference gives MBTS better scorch safety and less tendency to bloom. PolyBlueChem supplies Accelerator MBTS to a controlled specification with per-batch COA and SDS.

CAS number	120-78-5
Chemical name	2,2′-Dibenzothiazyl disulfide
Synonyms	Accelerator MBTS; DM; dibenzothiazyl disulfide; benzothiazyl disulfide; MBTS
Molecular formula	C₁₄H₈N₂S₄
Molecular weight	332.5 g/mol
Type	Thiazole accelerator (disulfide)
Appearance	White or light yellow powder

Chemistry and Structure

MBTS consists of two benzothiazole units joined by a disulfide (-S-S-) bridge. The structure explains its behaviour:

The benzothiazole rings are the active accelerator fragments; they accelerate sulfur vulcanisation once the disulfide opens.
The disulfide bridge makes MBTS more stable and less reactive than MBT, giving better scorch safety and less tendency to bloom.
The molecule contains no amine, so it does not raise the same nitrosamine concerns as amine-based accelerators.

Because it is a thiazole (not a sulfenamide), MBTS is not strongly delayed – it acts faster than the sulfenamides (CZ, TBBS, DCBS) but with more processing safety than MBT alone. It also acts partly as a sulfur donor through its disulfide group.

How MBTS Works as an Accelerator

In a sulfur cure, MBTS accelerates the formation of crosslinks between polymer chains. Its action can be summarised as:

Thiazole activity – the benzothiazole fragment reacts with sulfur and the rubber, speeding the vulcanisation reaction.
Disulfide/sulfur donation – the -S-S- group can participate in the crosslinking chemistry, so MBTS behaves partly as an accelerator and partly as a sulfur source.
Activator dependence – like other accelerators, MBTS needs the zinc oxide/stearic acid activator system and, usually, elemental sulfur; it is often used with a secondary accelerator such as DPG to raise activity.

MBTS is therefore a versatile “primary” or “secondary” accelerator: it can accelerate a compound on its own, or be blended with other accelerators to adjust the cure.

How Accelerator MBTS Is Produced

MBTS is made by oxidising 2-mercaptobenzothiazole (MBT), which couples two thiazole thiols into the disulfide:

MBT is dissolved or suspended in a suitable medium.
An oxidising agent (for example, hydrogen peroxide, chlorine or a hypochlorite system) oxidatively couples the thiols.
The disulfide product is filtered, washed, dried and milled to a powder.

Control targets complete coupling and low residual MBT, which would increase cure activity and reduce scorch safety. The specification therefore fixes melting point, heating loss, ash and sieve residue.

Specifications and Quality Control

Accelerator MBTS is supplied as a white or light yellow powder to the following specification:

Parameter	Specification
Appearance	White or light yellow powder
Initial melting point	165 °C min
Heating loss	0.30% max
Ash	0.30% max
Sieve residue (150 µm)	0.1% max

Parameter	What it controls
Initial melting point (165 °C min)	Purity and identity; MBTS has a characteristically high melting point
Heating loss (0.30% max)	Moisture/volatiles; affects weighing and processing
Ash (0.30% max)	Inorganic residues
Sieve residue (150 µm, 0.1% max)	Particle size / dispersion

A specification sheet and a per-batch certificate of analysis (COA) are available on request.

Key Properties

Property	Behaviour	Practical value
Class	Thiazole (disulfide)	General-purpose acceleration
Scorch safety	Better than MBT	Safer processing
Bloom	Less than MBT	Cleaner compound surface
Secondary use	Works with DPG and other accelerators	Flexible cure tuning
Amine content	None	No amine-derived nitrosamine concern

Applications

Industry / product	Function
Tyres	General accelerator in tyre compounds; secondary accelerator
Belts and hoses	Acceleration of technical rubber goods
Footwear and mouldings	General rubber goods
Mechanical goods	Seals, gaskets, industrial rubber
General rubber	NR, SBR, BR, NBR and blends

Tyres and technical goods – MBTS is used as a primary accelerator or, more often, as a secondary accelerator alongside a sulfenamide or with DPG, to tune cure rate and properties.
General rubber goods – an economical, versatile accelerator where the strong delay of a sulfenamide is not needed.

Accelerator MBTS vs Other Accelerators

Accelerator	CAS	Class	Delay / speed	Typical role
MBT (M)	149-30-4	Thiazole (thiol)	Fast, lower scorch safety	General accelerator; intermediate
MBTS (DM)	120-78-5	Thiazole (disulfide)	Medium; better scorch than MBT	General / secondary accelerator
CZ (CBS)	95-33-0	Sulfenamide	Delayed	Tyres and technical goods
TBBS (NS)	95-31-8	Sulfenamide	Delayed	Tyres; the common sulfenamide
DPG (D)	102-06-7	Guanidine	Fast	Secondary accelerator / activator

Guidance: use MBTS where a general-purpose, amine-free accelerator with good scorch safety is wanted; pair it with DPG to raise activity; choose a sulfenamide (CZ, TBBS, DCBS) when more delay and scorch safety are needed, as in tyres.

Dosage and Cure Systems

Use	Character
Primary accelerator	MBTS alone, with sulfur and activators
Secondary / booster	MBTS with DPG or a sulfenamide to raise cure rate
Sulfur-donor role	The disulfide can contribute to crosslinking, allowing lower elemental sulfur

Levels are set by the cure system and confirmed by rheometer and physical tests. As with any accelerator, MBTS works with zinc oxide and stearic acid activators and elemental sulfur.

Safety, Handling and Storage

Skin sensitisation – like most rubber accelerators, MBTS is a potential skin sensitiser (H317); avoid skin contact and follow good industrial hygiene.
Dust – avoid breathing the powder; use local extraction where large amounts are handled.
No amine – because MBTS contains no amine, it does not carry the amine-derived nitrosamine concern of some accelerators.
Storage – keep sealed, cool and dry, away from acids and oxidisers.

Regulatory Status

Use	Status (as commonly cited)
Rubber (industrial)	Governed by the buyer’s specification and article requirements
Food-contact / potable-water rubber	Only where the specific accelerator is permitted; confirm the applicable regulation

Packaging, Logistics and Supply

Item	Standard options
Packaging	25 kg PP/PE bags or fibre drums
Documentation	Per-batch COA and SDS
Incoterms	FOB and CIF
Storage	Sealed, cool and dry

Price tracks the MBT feedstock and the finishing quality; buying on committed tonnage gives the best terms.

MBT and MBTS: The Thiazole Pair

MBT and MBTS are closely related, and buyers often need to know which to use. MBT is 2-mercaptobenzothiazole (the thiol); MBTS is its disulfide (two MBT units joined by sulfur).

Comparison	MBT (M)	MBTS (DM)
Structure	Thiazole thiol	Thiazole disulfide
Cure activity	Faster, more active	More controlled
Scorch safety	Lower	Better
Bloom tendency	Higher	Lower
Typical role	Primary accelerator; MBT is also used in mineral flotation	Primary or secondary accelerator

Where a faster cure and full activity are wanted, MBT is chosen; where better scorch safety and less bloom are wanted, MBTS. In many compounds the two are interchangeable in function, with the choice made on processing behaviour and cost.

Quality: Reading an MBTS Certificate of Analysis

Parameter	What it tells you
Initial melting point (165 °C min)	Confirms a pure disulfide; residual MBT lowers it and raises activity
Heating loss (0.30% max)	Moisture/volatiles
Ash (0.30% max)	Inorganic residues
Sieve residue (150 µm, 0.1% max)	Dispersion; coarse material can cause cure defects

Residual MBT is the parameter to watch: it makes the accelerator more active and less scorch-safe, so a consistent, low-MBT batch is what delivers consistent cure.

MBTS in Tyre and Technical Compounds

MBTS is used both as a primary accelerator and, more often, as a secondary accelerator that tunes the cure of a compound.

Role	How MBTS is used
Primary accelerator	On its own with sulfur and activators, for general rubber goods
Secondary accelerator	With a sulfenamide (CZ/TBBS) to adjust cure rate and properties
With DPG	MBTS + DPG is a classic fast general-purpose system
Sulfur-donor contribution	The disulfide can contribute to crosslinking, allowing lower elemental sulfur

Because MBTS is versatile and forgiving, it is a common “utility” accelerator in a rubber plant: it can be used alone where the strong delay of a sulfenamide is unnecessary, or blended to fine-tune a cure system that is close but not quite right.

Scorch Safety, Bloom and Processing

Two practical behaviours distinguish MBTS from its thiazole parent MBT.

Scorch safety – MBTS is more stable than MBT, so it begins to cure later at processing temperature. This gives a wider processing window and reduces the risk of premature vulcanisation.
Bloom – MBTS is less prone to migrate to the surface of the compound than MBT, so it leaves a cleaner surface and wastes less of the addition. Bloom can spoil appearance and reduce the effective protection the compound retains.

For these reasons MBTS often replaces MBT where a slightly more controlled, cleaner-running accelerator is wanted, at a modest cost premium.

Accelerator Combinations with MBTS

System	Character	Where used
MBTS alone + sulfur	General-purpose cure	General rubber goods
MBTS + DPG	Faster, more active	Technical goods, footwear
MBTS + sulfenamide (CZ/TBBS)	Fine-tuned cure rate	Tyres and demanding goods
MBTS + thiuram (TMTD)	Low-sulfur / EV-type systems	Heat-resistant compounds

Accelerator combinations are chosen so that the total system delivers the required scorch time, cure rate and final crosslink density. Because MBTS is a thiazole (not strongly delayed), it is usually paired with a more delayed accelerator when a long processing window is needed, or with DPG when more speed is needed.

The Amine-Free Advantage

Because MBTS contains no nitrogen in an amine form, it does not raise the same nitrosamine concerns as amine-derived accelerators (sulfenamides from secondary amines, thiurams/dithiocarbamates).

Accelerator class	Nitrosamine potential
Sulfenamides from secondary amines	Higher concern
Sulfenamides from primary amines (CZ, TBBS)	Lower concern
Thiazoles (MBT, MBTS)	No amine-derived concern

This makes MBTS attractive where a plant wants to reduce nitrosamine potential in the cure system while keeping a versatile, effective accelerator.

MBTS in Practice and Selection

MBTS is the “utility” thiazole accelerator: it can stand alone or blend with almost anything, and it is chosen when a plant wants a reliable, amine-free accelerator with sensible processing safety.

Situation	Why MBTS fits
General rubber goods	Effective, versatile, economical
Need to boost a cure	Blends with DPG or a sulfenamide
Want less bloom than MBT	Lower bloom tendency
Want to avoid amine-derived nitrosamines	Amine-free thiazole

In a compound, MBTS is set with the sulfur level, the zinc oxide/stearic acid activators and any co-accelerator. Where the cure must be more delayed, a sulfenamide is used; where it must be faster, DPG or a thiuram is added. Because MBTS continues the thiazole line from MBT, plants that already use MBT can often swap to MBTS to gain scorch safety and reduce bloom with minimal reformulation – confirming the cure on the rheometer and the physical properties on the cured article.

As a rule: use MBTS when you need a general-purpose, amine-free accelerator; step up to a sulfenamide when you need more delay and scorch safety; add DPG when you need more speed.

Frequently Asked Questions about Accelerator MBTS (DM)

What is Accelerator MBTS used for?

It is a thiazole accelerator for sulfur vulcanisation, used in tyres, technical rubber goods and general rubber, often as a secondary accelerator.

What is the CAS number of MBTS?

120-78-5.

Is MBTS the same as DM?

Yes – MBTS and DM are names for the same accelerator, 2,2′-dibenzothiazyl disulfide.

How does MBTS differ from MBT?

MBT is the thiazole thiol; MBTS is its disulfide. MBTS usually gives better scorch safety and less bloom than MBT.

Does MBTS contain an amine?

No – it contains no amine, so it does not carry the amine-derived nitrosamine concern of some accelerators.

Does MBTS need activators?

Yes – it works with zinc oxide and stearic acid and elemental sulfur, and is often boosted with DPG.

Is MBTS a skin sensitiser?

Yes – like most accelerators it is a potential skin sensitiser; avoid skin contact.