Guaiacol CAS 90-05-1

What is Guaiacol?

Guaiacol is 2-methoxyphenol — catechol with one of its two hydroxyls capped as a methyl ether, C₇H₈O₂. That half-protected arrangement is the point: one free phenol to react with, one methoxy group fixed in place next to it, which is exactly the substitution pattern vanillin and guaifenesin are built on.

It is a clear, colourless to pale yellow liquid with a powerful smoky, medicinal odour, boiling near 205 °C. Its most awkward physical property is its melting point of about 26–29 °C: in a cool warehouse it is a crystalline solid, and in an Indian summer it is a liquid. Drum heating is a routine part of handling it, not an exception.

It darkens on exposure to air and light, as free phenols generally do, so colour is a storage property as much as a production one. It is only slightly soluble in water, miscible with ethanol, ether and chloroform, and it is hygroscopic enough that moisture specification matters in sensitive syntheses.

Commercially, guaiacol is a mid-volume specialty intermediate whose demand is anchored to two products: synthetic vanillin and the expectorant guaifenesin. Behind those sit smoke flavour formulations, fragrance work, eugenol chemistry and a long tail of fine chemical and veterinary uses.

Why guaiacol specifically

• One free phenol, one fixed ether. The mono-methylated catechol gives you a single reactive hydroxyl with the methoxy group already in place — which is why routes to vanillin and guaifenesin start here rather than at catechol.
• The ortho-methoxyphenol pattern. Vanillin, eugenol, isoeugenol and guaifenesin all carry it. Building it in later is more expensive than buying it in.
• A powerful odour at low levels. Its smoky, medicinal character is detectable in the low parts per billion, which makes it a workhorse in smoke flavour and fragrance formulation.
• Liquid handling with a solid's melting point. It is bought as a liquid but crystallises below about 28 °C, so handling is a design consideration from the first drum.

How Guaiacol is Manufactured

Guaiacol is made either by selectively methylating catechol or by routes starting from o-anisidine. Catechol methylation dominates commercially.

• Catechol methylation. Catechol is methylated with methanol or dimethyl sulphate under controlled conditions to cap one hydroxyl as the methyl ether. Selectivity is the whole challenge — over-methylation gives veratrole, under-conversion leaves catechol.
• o-Anisidine route. An alternative diazotises o-anisidine and hydrolyses the diazonium salt to the phenol. It is used where the feedstock economics favour it.
• Natural and lignin-derived routes. Guaiacol occurs in wood creosote and in lignin pyrolysis products, and some flavour-market material is still isolated this way for labelling reasons rather than cost.
• Purification. Fractional distillation separates guaiacol from catechol and veratrole. The solidification point and the distillation range on the COA are the practical measures of how well that separation ran.

Typical Commercial Specification

Figures below are representative of standard commercial grade. Pharmaceutical and flavour grades with tighter colour, moisture and catechol limits are available — send us the specification you work to and we will quote against it.

Physical & Chemical Properties

Reactivity in practice

A free phenol with a methoxy group next door. That single arrangement drives almost everything guaiacol is bought for:

• Electrophilic substitution para to the hydroxyl. Both substituents direct to the same position, which is why condensation with glyoxylic acid followed by oxidation gives vanillin so cleanly.
• Etherification of the free hydroxyl. Reaction with glycidol or 3-chloro-1,2-propanediol gives guaifenesin — a single etherification step onto the free phenol.
• Allylation to eugenol chemistry. Allyl ether formation and rearrangement open the route to eugenol and isoeugenol, which feed both fragrance and further vanillin chemistry.
• Methylation to veratrole. Capping the second hydroxyl gives 1,2-dimethoxybenzene — useful in its own right, and an impurity when it happens unintentionally.
• Air oxidation. Free phenols darken in air. The colour build is cosmetic in an industrial synthesis and a serious problem in a flavour or pharmaceutical application.

Guaiacol vs Catechol, Veratrole and the Downstream Products

Guaiacol sits in the middle of a short series defined by how many of catechol's two hydroxyls have been methylated. Knowing where a given molecule sits in that series tells you immediately what it can and cannot do.

Stated plainly: catechol has one hydroxyl too many and veratrole has one too few. Guaiacol is the useful middle member because it offers exactly one reactive site in exactly the right place, and both of its neighbours in the series turn up on its certificate of analysis as the things that should not be there.

Industries We Supply Guaiacol To

The same drum goes to a cough syrup plant, a flavour house and a fragrance compounder. What changes between them is not the CAS number but the grade, the colour limit and the documentation each sector expects.

Where Guaiacol is Used

Guaiacol is a specialty intermediate with two large anchors and a long tail of smaller uses. These are the end uses our customers buy it for.

In guaifenesin manufacture

Guaifenesin is guaiacol glyceryl ether, and it is made in essentially one step: the free phenolic hydroxyl is etherified with glycidol or with 3-chloro-1,2-propanediol. Because the route is so short, feedstock quality transfers almost directly into the API — residual catechol brings a second reactive hydroxyl into a reaction that expects one, and colour carries straight through into a syrup that is supposed to be clear.

In vanillin production

The dominant synthetic route condenses guaiacol with glyoxylic acid and oxidises the result to vanillin. The ring substitution does the work: the hydroxyl and the methoxy group direct the incoming group to the same position, so the right isomer forms without elaborate control. Flavour-market buyers typically specify catechol and veratrole tightly, because both propagate into the finished vanillin.

In flavour and fragrance work

Guaiacol is itself a flavour and fragrance material, used at parts-per-million levels for smoke, medicinal and leather notes. At those concentrations, odour purity is the entire specification — a trace of an off-note that would be invisible in a synthesis plant will be immediately obvious in a finished flavour, which is why flavour grade exists as a separate commercial product.

In fine chemical synthesis

Beyond its two main markets it feeds eugenol and isoeugenol chemistry, agrochemical intermediates and a range of veterinary and antiseptic preparations. These buyers are generally more price-sensitive and more tolerant on colour than the pharmaceutical and flavour trades.

Quality Control & Testing

Every lot is released against a batch-specific Certificate of Analysis. The methods behind the numbers are standard across the industry, and we are happy to share them or to work to your own in-house test protocol.

• Assay and impurity distribution — gas chromatography quantifying catechol and veratrole alongside the main component.
• Solidification point — the fastest meaningful check on an incoming drum, sensitive to almost any dilution.
• Water content — Karl Fischer titration. The material is hygroscopic and an open drum drifts.
• Colour — APHA / Hazen against a standard. Colour carries into guaifenesin syrups and flavour applications.
• Distillation range and refractive index — quick confirmations of identity and of how cleanly the fractionation ran.
• Odour evaluation — for flavour and fragrance grades, assessed against a retained reference, because no instrumental figure replaces it.
• Non-volatile residue and iron — relevant in pharmaceutical and food-contact service.

Common Process Problems & Likely Causes

When guaiacol causes trouble in a plant, the cause is usually one of a short list of things. This table is the shortcut our technical desk works through before anyone opens a complaint file.

Packaging, Storage & Shipping

• Standard packing. 200 kg net in lined MS or HDPE drums, with 1000 L IBCs for larger users.
• Melting point handling. Guaiacol crystallises below about 28 °C. Plan for drum heaters, a warm room or a heated transfer line as part of normal handling — and melt gently, because local overheating drives colour.
• Air and light exclusion. As a free phenol it darkens in air and light. Keep drums sealed and headspace minimal; nitrogen-blanket bulk storage where colour matters.
• Storage. Cool, dry, well-ventilated and bunded, protected from light, away from oxidising agents and strong acids and bases.
• Materials of construction. Stainless steel, lined steel or suitable plastics. Avoid iron contact, which drives colour through phenol-iron complexation.
• Odour management. The odour is powerful and persistent at very low concentrations. Store away from other ingredients that could pick it up, and expect it to be noticeable around any open transfer.
• Shelf life. Typically 12 to 24 months in unopened original packing under those conditions. Beyond that, re-test colour and assay rather than assume.
• Transport classification. Generally shipped as a non-dangerous good for most modes; the flash point near 82 °C puts it above the flammable liquid threshold. Confirm against the current SDS and the shipper's declaration for your destination and mode.

Hazards & Safe Handling

Guaiacol is harmful if swallowed and irritates the skin, eyes and respiratory tract. It is a combustible liquid with a powerful, persistent odour. It must be handled by trained personnel under a proper risk assessment — the current SDS supplied with your consignment is the governing document.

• Skin and eye contact. It is a phenolic compound and irritates on contact. Chemical-resistant gloves rated for phenols, chemical goggles and a face shield for transfer operations.
• Vapour exposure. Vapour and mist exposure rises sharply when the material is warmed for transfer, which is exactly when most handling happens. Local exhaust ventilation at transfer points, not just general room ventilation.
• Odour as a warning and a nuisance. The odour is detectable far below any hazardous concentration, so smelling it does not mean you are overexposed — but it does carry, taints nearby materials and generates complaints.
• Fire. A combustible liquid with a flash point near 82 °C. Keep away from heat, sparks and open flame, and bear in mind that heated transfer brings the material closer to its flash point.
• Incompatibilities. Strong oxidising agents, strong acids and bases, and ferric salts. Iron contact is a quality issue as much as a chemistry one.
• Spill response. Contain, absorb with inert non-combustible material and collect in a labelled closed container. Ventilate thoroughly — the odour persists long after the spill is cleaned up.
• Environment. Harmful to aquatic life. Do not allow to enter drains, surface water or groundwater. Dispose through a licensed chemical waste contractor.
• First aid. Remove contaminated clothing immediately, wash skin with plenty of water and soap, flush eyes for at least 15 minutes, and seek medical attention with the SDS to hand.

Regulatory & Compliance Notes

Guaiacol is an established industrial, pharmaceutical and flavour chemical, listed on the major national chemical inventories. Because obligations differ by territory, volume and use, the notes below are orientation rather than legal advice — confirm your own position with your regulatory adviser before importing.

• Inventory status. Listed on the principal chemical inventories in the major importing regions. Ask us for the inventory confirmation relevant to your destination country.
• Flavour use. Guaiacol is a recognised flavouring substance in the major food regulatory systems, and smoke flavour preparations built on it are separately regulated. Flavour-grade material and the supporting statements are quoted separately from technical grade.
• Pharmaceutical use. Where the material feeds a regulated drug substance such as guaifenesin, the catechol and colour limits may form part of your marketing authorisation rather than merely a purchase specification. Agree them in writing.
• Import registration. Several territories require the importer to hold a registration or notification before a consignment lands. Start that process early — it is the most common cause of delay at destination.
• Hazard communication. Supplied with an SDS compliant with the format applicable to your region, and labelled in line with the GHS classification for the product.
• Dangerous goods. Generally not restricted for transport given the flash point near 82 °C. Confirm against the current SDS; declarations prepared for IMDG (sea) or IATA (air) where a destination requires them.

We Supply Guaiacol Worldwide

Chelora Chemicals is a supplier and export partner, not a single-plant trader. We ship Guaiacol from India to customers across Asia, Europe, the Middle East, Africa, and North and South America, handling the export documentation, heated-transfer arrangements where required and freight so the material arrives ready to use.

• Incoterms. EXW, FOB, CIF, CFR and DAP quoted to suit your purchasing terms and freight arrangements.
• Ports. Regular shipments through Nhava Sheva (JNPT) and Mundra, with other Indian ports arranged where it suits the routing.
• Documentation. Commercial invoice, packing list, certificate of origin, COA, SDS and food or pharmaceutical grade statements where applicable issued as a complete set.
• Flexible volumes. A single drum for laboratory qualification, through LCL consolidations, up to repeat full loads on a supply contract.
• Supply continuity. Because we are independent of any one producer, a plant turnaround or a shipping disruption at one source does not have to become your stock-out.

Buying Guaiacol from Chelora

We are an independent sourcing and supply partner. For guaiacol that means settling two things at enquiry: the catechol and colour limits your process actually needs, and whether the material is going into pharmaceutical, flavour or technical service — because the grade and the price differ sharply between them.

• Documentation on every lot. Batch-specific COA including catechol, veratrole, colour and solidification point, current SDS and TDS.
• Samples before commitment. Trial quantities for process or flavour qualification ahead of a commercial order.
• Quantities. From a single 200 kg drum through to IBC and tank quantities on contract supply.
• Handling guidance. Practical advice on melting, heated transfer and colour protection, which is where most first-time users lose material.
• Export experience. Packing, labelling and export documentation handled for sea and road freight.
• Related intermediates. 4-Aminophenol, salicylic acid and the wider pharmaceutical intermediate range from one supplier.

How ordering works

• Send the enquiry. Product, grade or pharmacopoeia standard, quantity, destination port and the Incoterm you buy on. If you have a spec sheet, attach it — it saves a round trip.
• We quote. Price, lead time, packing and a sample COA, normally within one working day.
• Sample and qualify. For first orders or critical applications, we send a trial quantity so your lab can sign off before you commit.
• Confirm the order. Proforma invoice issued; payment terms agreed against the volume and the relationship.
• Production and QC. Material allocated and released against a batch-specific COA, with a pre-shipment sample where the application calls for it.
• Ship and document. Packed, labelled and loaded with the full export document set, and tracked through to arrival.

Related Pharmaceutical Intermediates & Excipients

Buyers of guaiacol usually source several of these alongside it. Consolidating them on one order cuts freight cost and gives you a single point of contact for documentation.