What Is Butylated Hydroxytoluene (BHT)?
Butylated hydroxytoluene (BHT), CAS 128-37-0, chemically 2,6-di-tert-butyl-4-methylphenol (also called Antioxidant 264 or DBPC), is a hindered phenolic antioxidant. It is one of the most widely used antioxidants in the world, protecting rubber, plastics, oils, fuels and other organic materials against oxidation and heat ageing, and is also used as a food and feed antioxidant where the appropriate grade is specified.
BHT is a single-ring hindered phenol: it is a small, crystalline, high-purity molecule. That gives it two advantages – excellent solubility and fast action – and one limitation: because it is small and relatively volatile, it can be lost at very high processing temperatures, where a higher-molecular-weight antioxidant is preferred. PolyBlueChem supplies BHT to a controlled specification with per-batch COA and SDS.
| CAS number | 128-37-0 |
| Chemical name | 2,6-Di-tert-butyl-4-methylphenol |
| Synonyms | Butylated hydroxytoluene; BHT; Antioxidant 264; DBPC; 2,6-di-tert-butyl-p-cresol |
| Molecular formula | C15H24O |
| Molecular weight | 220.35 g/mol |
| Type | Hindered phenolic antioxidant |
| Appearance | White crystalline powder |
| Food additive number | E321 (where a food-grade material is used) |
Chemistry and Structure
BHT is a phenol carrying a methyl group para to the hydroxyl and two bulky tert-butyl groups at the two positions flanking (ortho to) the hydroxyl. This substitution pattern is the essence of a hindered phenol:
- The phenolic -OH is the active group that scavenges radicals.
- The two tert-butyl groups shield the -OH sterically. That shielding is why BHT is a “hindered” phenol: it reacts with damaging peroxy radicals but does not readily undergo side reactions that would discolour the material.
- The molecule is small (MW 220), so it dissolves easily and acts quickly, but it is more volatile than the higher-MW antioxidants and can be lost at high temperatures.
BHT is non-staining and non-discolouring, which is why it can be used in white and light-coloured materials as well as in oils and food-contact applications.
How BHT Works as an Antioxidant
Organic materials age by autoxidation: heat, light or metal traces generate radicals, and peroxy radicals (ROO•) propagate a chain that eventually degrades the material (hardening, cracking, gumming, discolouration). BHT interrupts this chain:
- The phenolic -OH donates a hydrogen atom to a peroxy radical, giving a stable hydroperoxide and turning BHT into a stabilised phenoxy radical.
- The phenoxy radical is resonance-stabilised and unreactive, so it does not continue the chain.
- Because the antioxidant is consumed as it protects, its effect is measured as the length of the induction period it gives for a given loading.
BHT is a primary (chain-breaking) antioxidant. Like other phenolics, it is often combined with a secondary (hydroperoxide-decomposing) antioxidant – a phosphite or thioester – so that the hydroperoxides it leaves behind are also removed (synergism).
How BHT Is Produced
BHT is made by the alkylation of p-cresol (4-methylphenol) with isobutylene (isobutene) in the presence of an acid catalyst. The reaction places two tert-butyl groups at the positions flanking the hydroxyl:
- p-Cresol and isobutylene are reacted under acid catalysis.
- The tert-butyl groups are introduced ortho to the -OH, giving 2,6-di-tert-butyl-4-methylphenol.
- The crude product is distilled or crystallised, then flaked or milled to the white crystalline powder.
Because BHT is used in food and feed as well as in industry, purification matters: the specification controls free phenol, residue on ignition, moisture, sulfide and trace metals (arsenic and heavy metals), which reflect the purity needed for sensitive applications.
Specifications and Quality Control
BHT is supplied to the following specification:
| Parameter | Specification |
|---|---|
| Appearance | White crystalline powder |
| Initial melting point | 69 – 70 °C |
| Free phenol | 0.02% max |
| Residue on ignition | 0.005% max |
| Moisture | 0.05% max |
| Sulfide | 0.002% max |
| Arsenide (As) | 1 mg/kg max |
| Heavy metal | 5 mg/kg max |
Each parameter controls a specific quality risk:
| Parameter | What it controls |
|---|---|
| Initial melting point (69-70 °C) | Purity and identity; a sharp, correct melting point confirms a clean product |
| Free phenol (0.02% max) | Unreacted p-cresol; affects odour and purity |
| Residue on ignition (0.005% max) | Inorganic residues; the very low limit reflects high purity |
| Moisture (0.05% max) | Water content; affects handling and quality |
| Sulfide (0.002% max) | Sulfur-containing impurities |
| Arsenide and heavy metal | Toxic-metal limits for sensitive (including food) use |
A specification sheet and a per-batch certificate of analysis (COA) are available on request.
Key Properties
| Property | Behaviour | Practical value |
|---|---|---|
| Function | Chain-breaking antioxidant | Protects against oxidation and heat ageing |
| Form | White crystalline powder | Easy to weigh, dissolve and disperse |
| Solubility | Good solubility in oils and organic media | Effective in oils, fats and polymers |
| Colour | Non-staining, non-discolouring | Suits white and light-coloured materials |
| Volatility | Relatively high (low MW) | Fast action; can be lost at very high temperatures |
Applications
BHT is used across rubber, plastics, oils and food/feed. The table maps the main uses.
| Industry | Function |
|---|---|
| Rubber | Anti-ageing protection of natural and synthetic rubber |
| Plastics and resins | Thermal-oxidative stabilisation of polyolefins and styrenics |
| Oils, fuels and lubricants | Oxidation inhibitor; prevents gumming and acid build-up |
| Food and feed | Antioxidant (E321) where a food-grade material is specified |
| Adhesives, coatings and inks | Stabilisation against ageing |
| Cosmetics and personal care | Antioxidant where permitted |
- Rubber and plastics – BHT protects the polymer during processing and service; it is popular for processing stabilisation and for materials where a volatile, fast-acting antioxidant is acceptable.
- Oils and fuels – BHT prevents oxidative breakdown and gum formation in lubricants, greases, fuels and transformer oils.
- Food and feed – as E321, BHT slows rancidity in fats and oils; a food-grade material must be used and permitted in the market.
- Adhesives and coatings – protects the binder against ageing.
BHT vs Other Antioxidants
BHT is compared with the higher-MW hindered phenolics and with amine antioxidants.
| Antioxidant | CAS | Type | Volatility | Staining | Typical role |
|---|---|---|---|---|---|
| BHT (264) | 128-37-0 | Hindered phenolic (mono) | Relatively high | Non-staining | Oils, plastics, food; fast action |
| Antioxidant 2246 | 119-47-1 | Hindered phenolic (bis) | Low | Non-staining | Rubber, latex, high-temp processing |
| Antioxidant 1010 | 6683-19-8 | Hindered phenolic (tetrakis) | Very low | Non-staining | High-MW plastics |
| Antioxidant RD (TMQ) | 26780-96-1 | Amine (quinoline) | – | Staining | Tyres, dark goods |
- Want fast, inexpensive, non-staining protection? BHT.
- High-temperature processing or long service life? A higher-MW phenolic (2246, 1010) that resists volatilisation.
- Oils, fats and food? BHT (E321 where permitted) is well established.
- Strong dynamic protection in dark rubber? An amine antioxidant (RD, 6PPD).
Dosage and Use
Levels are application-specific and confirmed by tests. The figures below are orientation only.
| Application | Starting-point guidance |
|---|---|
| Plastics | Low percentages of the polymer weight |
| Oils, fuels and lubricants | A small fraction of a percent, set by the oxidation test |
| Rubber | A few phr, adjusted for service temperature |
| Food and feed | Set by the permitted level for the specific food and market |
Because BHT is volatile, do not over-rely on it for very high melt temperatures; where losses are a concern, use it combined with or replaced by a higher-MW antioxidant.
Food and Feed Use (E321)
BHT is an authorised food antioxidant (E321) in many markets, used to retard rancidity in fats, oils and foods. Food use requires a food-grade material that meets the toxic-metal limits in the specification and the permitted dosage for the market.
| Point | Note |
|---|---|
| Grade | A food-grade material must be specified; confirm the grade before ordering |
| Limits | Arsenic 1 mg/kg max and heavy metal 5 mg/kg max support sensitive use |
| Dosage | Governed by the permitted level in the destination market |
For any food or feed use, confirm that BHT and the specific dosage are permitted in your market.
Safety, Handling and Storage
- Low hazard – BHT is of low acute toxicity and has a long history of use in food, rubber and plastics.
- Dust – avoid breathing the powder; use dust control where large amounts are handled.
- Hygiene – good industrial hygiene; wash after contact.
- Storage – keep sealed, cool and dry; away from strong oxidisers and strong odours.
Regulatory Status
| Use | Status (as commonly cited) |
|---|---|
| Food antioxidant | E321 where authorised; dosage limits apply per market |
| Feed antioxidant | Permitted in many markets; confirm the local rule |
| Industrial (rubber, plastics, oils) | Governed by the buyer’s specification |
Packaging, Logistics and Supply
| Item | Standard options |
|---|---|
| Packaging | 25 kg PP/PE bags or fibre drums (or as agreed) |
| Documentation | Per-batch COA and SDS |
| Incoterms | FOB and CIF |
| Storage | Sealed, cool and dry |
BHT is a high-volume specialty antioxidant; price tracks the p-cresol/isobutylene feedstock and the purity grade. Buying on committed tonnage gives the best terms.
BHT in Oils, Fuels and Lubricants
Oils and fuels oxidise in storage and service, forming acids, gums and sludge. BHT is a classic inhibitor for these systems because it dissolves readily in oil and acts quickly.
| System | Why BHT is used |
|---|---|
| Lubricating oils and greases | Prevents oxidative thickening and acid formation |
| Fuels (gasoline, diesel, biodiesel) | Stabilises against gum and sediment formation in storage |
| Transformer and insulating oils | Slows oxidation that would raise acidity and reduce life |
| Fats and edible oils | Retards rancidity (E321, food grade) |
In oil, the antioxidant is judged by the induction period in an accelerated oxidation test (for example a Rancimat or oxygen-absorption test). Because BHT is consumed as it protects, the dose is set to give the required storage or service life with a margin.
BHT in Plastics and Polymer Stabilisation
In polymers, BHT is used both as a processing stabiliser (protecting the melt) and as a long-term antioxidant. Its good solubility helps it distribute evenly through the polymer.
| Function in plastics | Role of BHT |
|---|---|
| Processing stabilisation | Prevents degradation during extrusion and moulding |
| Long-term stabilisation | Protects the finished article against heat and oxygen |
| Colour retention | Non-staining, so it does not tint the polymer |
Where a plastic is processed at very high temperature or needs a very long service life, BHT’s volatility is the limiting factor: at those temperatures a higher-molecular-weight phenolic (such as 2246 or 1010) is often preferred, sometimes with BHT retained for fast initial protection.
Combining BHT with Secondary Antioxidants
As a chain-breaking (primary) antioxidant, BHT deals with peroxy radicals but leaves hydroperoxides. A secondary antioxidant – a phosphite (for processing) or a thioester (for long-term heat ageing) – removes those hydroperoxides, and the combination is more effective than either alone.
| Component | Role | Examples |
|---|---|---|
| Primary (chain-breaking) | Scavenges peroxy radicals | BHT, 2246, 1010 (hindered phenolics) |
| Secondary (hydroperoxide-decomposing) | Removes hydroperoxides | Phosphites; thioesters (thiodipropionates) |
A typical polymer stabiliser package therefore pairs BHT (or another phenolic) with a phosphite and/or a thioester, tuned to the processing temperature and the required service life.
Quality and Purity: Why the COA Matters
BHT is sold at different purity levels, and the specification is what separates a good-grade material from a cheap one. For food and feed use, and for polymers where colour matters, the trace limits are the important part of the certificate.
| Parameter | Why it matters to the buyer |
|---|---|
| Initial melting point | Confirms a clean, high-purity product |
| Free phenol | Low residual p-cresol means low odour and better purity |
| Residue on ignition | Very low ash keeps the material clean in sensitive uses |
| Moisture | Affects weighing and storage stability |
| Arsenide and heavy metal | Essential for food/feed and other sensitive applications |
Always buy against a written specification and check the batch COA, especially for food-contact or food-additive use.
Choosing Between BHT and Higher-Molecular-Weight Phenolics
BHT and the higher-molecular-weight hindered phenolics (2246, 1010) do the same chemical job, but they behave differently in the plant and in service. The choice depends on processing temperature, service life, cost and where the antioxidant has to stay.
| Factor | BHT (264) | Higher-MW phenolic (e.g. 2246, 1010) |
|---|---|---|
| Molecular weight | 220 (small) | 340-1,200 (larger) |
| Volatility | Relatively high | Low |
| Processing losses | Possible at very high melt temperatures | Minimal – stays in the polymer |
| Cost | Low | Higher |
| Best for | Oils, fats, fast processing stabilisation, food/feed | High-temperature processing, long service life, rubber and latex |
A practical approach is often to use both: BHT for fast, inexpensive protection and a higher-MW phenolic where the material will see high temperature or a long, hot service life. For food, feed and oil applications where the antioxidant is used at a permitted low level in an oily medium, BHT remains a first choice.
Frequently Asked Questions about BHT
What is BHT?
Butylated hydroxytoluene, CAS 128-37-0, a hindered phenolic antioxidant (2,6-di-tert-butyl-4-methylphenol).
Is BHT the same as Antioxidant 264?
Yes – “264” is a common trade designation for BHT.
What is BHT used for?
As an antioxidant in rubber, plastics, oils, fuels, adhesives and (as E321) in food and feed where permitted.
Does BHT stain or discolour?
No – it is non-staining and non-discolouring.
Is BHT volatile?
It is more volatile than higher-MW antioxidants; at very high processing temperatures a higher-MW phenolic may be preferred.
Can BHT be used in food?
It is authorised as E321 in many markets, but only with a food-grade material, within permitted levels, and where allowed locally.
How is BHT stored?
Sealed, cool and dry, away from strong oxidisers.
Related reading
- Butylated hydroxytoluene (BHT) in rubber and plastics
- Rubber antioxidants and accelerators: selection guide
- Antioxidant 2246: properties and applications
- Antioxidant RD (TMQ): properties and applications
- Butylated hydroxytoluene (BHT, CAS 128-37-0) – product page
PolyBlueChem supplies Butylated hydroxytoluene (BHT, CAS 128-37-0) to a controlled specification, with per-batch COA and SDS and FOB/CIF delivery. Contact us with your grade, tonnage and delivery port.