Is dodecylbenzenesulfonic acid a single defined substance?

Commercially it is not. The alkylbenzene feedstock is a mixture of chain lengths around twelve carbons, and within each chain the aromatic ring can be attached at different positions, so the product is a family of closely related molecules rather than one compound. That is why more than one registry entry is in circulation for what is sold under the same trade description. Ask the supplier which identifier applies to the grade being quoted and make sure your safety data sheet, your specification and your own registration records all use the same one.

What does the figure in a grade name such as LABSA 96 refer to?

It refers to active matter, meaning the proportion of the product that is the sulfonic acid itself, with the remainder made up of water, residual sulfuric acid and unsulfonated organic material. It is a composition figure, not a quality ranking. A higher active matter figure means less water to pay for and transport, but it says nothing on its own about colour, about how much free sulfuric acid is present, or about the unsulfonated fraction that will float out in the finished product.

Why is the neutralisation exotherm treated as a hazard?

Because a strong acid reacting with a strong base releases heat quickly, and both the acid and the resulting paste are viscous, which makes mixing slow and local hot spots easy to create. Heat that is generated faster than it can be dispersed causes colour development, and in the worst case degradation and an uncontrolled rise in temperature. The standard controls are adding the acid to the base rather than the reverse, cooling, controlled addition rate, genuine mixing rather than stirring, and monitoring temperature continuously during the addition.

Which base should be used for neutralisation?

That depends on the salt you want. Sodium hydroxide gives the sodium salt used in most powders and liquids. Sodium carbonate gives the same salt but evolves carbon dioxide, which foams the batch and has to be vented and allowed for in vessel sizing. Ammonia and amines such as triethanolamine give salts with different solubility, clarity and skin-feel characteristics, which is why they appear in liquid and personal-care formulations. The choice also changes the electrolyte balance and therefore the viscosity of the finished product.

What should be checked on receipt?

Active matter, free sulfuric acid, unsulfonated matter, water content and colour, each against the agreed method, plus a visual check of the container and its liner. Free sulfuric acid drives the amount of base you will need and the salt load you end up with; unsulfonated matter affects clarity and odour in the finished product; colour is the parameter most likely to drift and the hardest to correct later. Keep retained samples so that a colour or odour complaint can be traced to a specific lot.

Dodecylbenzenesulfonic acid: buying it, neutralising it

Technical article · Eapearl Chemical · 13 July 2026

This is one of the few raw materials that most buyers convert chemically before they use it. It arrives as a corrosive acid and does its work as a salt, and nearly every problem with it happens in the step between those two states.

One name, several registry entries

The product is made by sulfonating linear alkylbenzene, and the feedstock for that reaction is not a single compound. Commercial alkylbenzene is a distribution of alkyl chain lengths centred near twelve carbons, and within each chain length the aromatic ring can be attached at any of several positions along it. The sulfonic acid that results is therefore a family of related molecules, not one substance with one structure.

The practical consequence is administrative rather than chemical. More than one registry number circulates for material sold under the same description: an entry for dodecylbenzenesulfonic acid, commonly cited as CAS 27176-87-0, sits alongside entries written as alkyl derivatives covering a stated range of chain lengths. These are not interchangeable on paper even when the drums are equivalent in practice. Ask which identifier applies to the grade you are quoted, and make sure that the number on the safety data sheet, the number on your specification and the number in your own regulatory records are the same number.

Branched material, made from a branched alkylbenzene rather than a linear one, is a different case again and is restricted or disfavoured in many markets on biodegradability grounds. If linear feedstock matters to you, say so in the specification instead of assuming it.

What the chain distribution actually does

The molecule has the classic surfactant architecture: a hydrophilic sulfonic acid group on an aromatic ring, and a lipophilic alkyl chain. The balance between the two governs everything the material does, and the chain length distribution shifts that balance.

Longer average chain — better removal of oily soil, lower solubility in cold water, greater tendency to leave a finished liquid hazy at low temperature.
Shorter average chain — easier solubility and better cold stability, with less detergency against greasy soils.
Isomer distribution — attachment near the middle of the chain behaves differently from attachment near its end, affecting foam character and solubility in ways that two lots with identical active matter figures can still differ in.

This is why a change of supplier can pass every specification line and still change how a finished cleaner foams or how it looks after a cold night in a warehouse. Where those attributes matter, agree the chain length distribution as a specification item rather than inferring it from active matter.

What the specification has to pin down

Five lines carry most of the commercial risk, and each needs a stated test method beside it.

Active matter is the sulfonic acid content and sets the dosing basis for every formulation you make from it. Free sulfuric acid is the residue of the sulfonation step; it consumes base during neutralisation and converts into sodium sulfate, which is inert filler in a liquid and an unplanned electrolyte that can move viscosity. Unsulfonated matter, sometimes called free oil, is alkylbenzene that never reacted; it contributes nothing, and it is the usual reason a clear liquid formulation turns cloudy or develops an odour. Water content completes the mass balance and should reconcile with the other figures. Colour, reported on whichever scale both parties have agreed, is the parameter most likely to drift lot to lot, and it is effectively impossible to correct downstream in a product that has to look clean.

A certificate that reports active matter and nothing else has described a quarter of the material. Ask for the full set, and keep the results so that a trend is visible before it becomes a complaint.

Neutralisation is where batches are lost

Neutralisation looks like the simplest unit operation in the plant and produces more spoiled batches than any other step in this chemistry. The reaction between a strong acid and a strong base is fast and strongly exothermic, and both the incoming acid and the resulting paste are thick, so heat released at the point of addition does not disperse on its own.

Add the acid to the base, not the reverse, so that the acid is always the minority component entering a large, well-mixed and buffered volume.
Control the addition rate against the measured temperature of the batch, and stop the addition rather than chase a rising trend with more cooling.
Mix properly. A viscous paste needs genuine bulk movement; a stirrer that turns the middle of a vessel while the walls stay still will produce local over-acidity and local overheating at the same time.
Take the pH endpoint on a diluted sample, using a method agreed in advance, because a reading taken directly in a concentrated paste is not comparable between operators or between shifts.
Allow for gas if a carbonate base such as soda ash is used, since carbon dioxide evolution foams the batch and the vessel has to be sized and vented for that.
Record the base consumed. A batch that needed unusually more or less base than the previous one is telling you that the incoming free acid figure moved, which is worth investigating before the next delivery arrives.

Overshooting on either side has consequences. Left acidic, the product corrodes packaging and fails a specification that customers do check. Driven strongly alkaline, it can hydrolyse other ingredients in the formulation and is harsh on skin in a product intended for hand use.

A corrosive acid in the yard

Handle the incoming material as the corrosive liquid it is: appropriate eye and skin protection, no mixing with anything until the neutralisation procedure is running, and cleaned or dedicated transfer equipment. Materials of construction should be selected for a strong organic sulfonic acid rather than assumed from experience with the neutralised salt, and elastomer seals and hoses deserve a specific compatibility check.

The material is highly viscous and becomes more so as it cools, so unloading in winter needs a plan made before the vehicle arrives rather than improvised at the gate. Store it away from bases, including sodium hydroxide, and away from anything oxidising. Keep containers closed, since the material picks up water from humid air, and keep retained samples from every lot.

Ordering notes and recurring mistakes

The mistakes repeat across the industry: ordering on active matter alone and then discovering that free sulfuric acid changed the salt load; treating linear and branched material as equivalent; assuming that two registry numbers describing the same commercial product make the paperwork optional; sizing a neutralisation vessel with no allowance for foam; and qualifying a new lot on paper rather than by making a batch. State the salt you intend to produce, the base you will use and the appearance requirement of the finished product on the enquiry. Specifications, lot certificates and samples for grades such as LABSA 96 are issued against a named application through the contact page.