Introduction to Didecyl Dimethyl Ammonium Chloride (DDAC)
Didecyl dimethyl ammonium chloride (DDAC, CAS 7173-51-5) is a cationic quaternary ammonium compound (a “quat”) and one of the workhorse biocides of industry. Supplied as an 80% aqueous solution, it is a broad-spectrum antimicrobial and a cationic surfactant, used in disinfectants and sanitisers, water treatment, wood preservation, oilfield and industrial water systems, and cleaning products.
DDAC belongs to the quaternary ammonium biocide family, alongside benzalkonium chloride (BAC) and other dialkyl-dimethyl quats. Its two long C10 alkyl chains give it strong surface activity and antimicrobial power; its cationic charge controls both how it works and how it must be formulated. This article covers the identity, properties, mechanism, production, specification, applications, compatibility and sourcing of DDAC.
PolyBlueChem can supply DDAC 80% (CAS 7173-51-5); see the product page for the current specification.
Chemical Identity and Structure
DDAC is a quaternary ammonium salt in which the nitrogen atom carries four organic groups: two methyl groups and two n-decyl (C10) chains, with a chloride counter-ion. The molecule therefore has two permanent positive charges’ worth of character — a cationic head and two lipophilic tails — which is the classic architecture of a cationic surfactant and biocide.
| Property | Value |
|---|---|
| Common name | DDAC; didecyl dimethyl ammonium chloride |
| Other names | Didecyldimethylammonium chloride; quaternary ammonium compound (QAC) |
| CAS number | 7173-51-5 |
| Molecular formula | C22H48ClN |
| Molecular weight | Approx. 362.1 g/mol |
| Class | Cationic quaternary ammonium biocide / surfactant |
| SMILES | CCCCCCCCCC[N+](C)(C)CCCCCCCCCC.[Cl-] |
Physical and Chemical Properties
| Property | Typical value / behaviour |
|---|---|
| Appearance | Light yellow to white transparent liquid (80% solution) |
| Active matter | ≥ 80% (standard solution grade) |
| Ionic character | Cationic |
| pH (1% aqueous solution) | 4 – 8 |
| Water solubility | Fully miscible with water (as supplied) |
| Free amine and amine salt | ≤ 2% |
| Compatibility | Incompatible with anionic surfactants and strong oxidisers |
The 80% solution is a convenient, pourable liquid that dilutes readily in water to the use concentration. Its cationic character is the single most important formulation fact: DDAC will interact with, and can be precipitated or inactivated by, anionic materials.
How Quaternary Ammonium Biocides Work
DDAC kills micro-organisms by a physical, membrane-disrupting mechanism rather than by attacking a specific enzyme:
- Adsorption. The positively charged nitrogen head adsorbs onto the negatively charged surface of bacteria, fungi and algae.
- Penetration. The lipophilic alkyl chains insert into and disrupt the cell membrane.
- Leakage and lysis. Loss of membrane integrity causes leakage of cell contents and death of the organism.
Because this is a physical disruption of the membrane, QACs are effective against a broad range of bacteria (gram-positive and gram-negative), fungi, yeasts and algae, and resistance develops more slowly than with single-target antibiotics. Two practical consequences follow. First, QACs work best in clean systems, because soil and organic matter can consume them. Second, because they act at surfaces, good contact and adequate concentration matter as much as the intrinsic potency of the biocide.
DDAC’s two long chains give it particularly high surface activity and antimicrobial power among the QACs, which is why it is used at relatively low active concentrations in disinfectants, algaecides and preservatives.
Product Forms and the 80% Solution
DDAC is normally traded as a concentrated aqueous solution rather than as a solid:
- 80% active solution. The standard commercial grade — a light yellow to white transparent liquid, easy to dilute and dose.
- Lower-active dilutions. Solutions of 50% or other strengths are also supplied for convenience or for regulatory purposes.
- Blends. DDAC is frequently blended with other QACs (such as BAC) or with non-ionic surfactants and solvents to give ready-to-use disinfectant and cleaning concentrates.
Because the product is a liquid solution, handling is simple, but the active content must be checked, because dosing calculations and regulatory limits are expressed in terms of active QAC.
Industrial Production
DDAC is made by quaternisation: a tertiary amine (N,N-dimethyldecylamine) is alkylated with a decyl halide (decyl chloride), converting the tertiary amine into a quaternary ammonium salt. The reaction is a straightforward nucleophilic substitution whose economics depend on the availability of the C10 amine and halide and on achieving complete quaternisation with low residual amine.
| Stage | Purpose | Notes |
|---|---|---|
| 1. Feedstocks | Provide the amine and alkylating agent | N,N-Dimethyldecylamine and decyl chloride (or an equivalent alkyl halide) |
| 2. Quaternisation | Form the quaternary ammonium salt | Tertiary amine + alkyl halide; controlled temperature; polar solvent as needed |
| 3. Completion and adjustment | Minimise residual amine | Reaction control to keep free amine and amine salt within the specification limit |
| 4. Dilution / standardisation | Reach the target active content | Adjustment to the 80% (or other) active solution; pH adjustment |
| 5. Quality control | Confirm the specification | Active content (titration), appearance, free amine, pH |
The “free amine and amine salt” limit in the specification is a direct measure of how completely the quaternisation has gone: residual amine is both a quality issue and relevant to odour and compatibility.
Specifications and Quality Control
The commercial 80% grade is controlled by active content, appearance, residual amine and pH. A representative specification is shown below.
| Parameter | Typical specification |
|---|---|
| Product | Didecyl dimethyl ammonium chloride 80% |
| Active matter | ≥ 80% |
| Appearance | Light yellow to white transparent liquid |
| Free amine and amine salt | ≤ 2% |
| pH (1% aqueous solution) | 4 – 8 |
Quality control centres on the active content (by titration), the residual amine and the pH. The appearance — a clear, light liquid — is a useful first check, since haziness or darkening can indicate contamination or ageing.
Applications: Disinfectants and Sanitisers
DDAC’s largest use is as a biocide in disinfectants and sanitisers for hard surfaces and equipment, in healthcare, food-service, institutional and household settings. It is valued because it is effective against a broad spectrum of organisms, is less corrosive and less odorous than many alternatives, and is compatible with non-ionic surfactants in cleaning concentrates.
- Hard-surface disinfectants. Active biocide in hospital, food-processing and household disinfectant concentrates, often blended with a non-ionic surfactant.
- Food-contact and equipment sanitisers. Used where permitted by local regulation for sanitising food-contact surfaces and equipment.
- Antimicrobial cleaning products. Combined with detergents to give both cleaning and microbial control.
- Preservation of formulated products. As an antimicrobial preservative in aqueous technical products.
Applications: Water Treatment, Wood, Oilfield and More
- Water treatment. DDAC is an algaecide and biocide in cooling towers, recirculating water, pools and industrial water systems, controlling algae, bacteria and slime.
- Wood preservation. As a component of wood preservative systems, protecting timber against fungal and insect attack.
- Oilfield and industrial fluids. Used as a biocide to control sulphate-reducing and other bacteria in oilfield waters and industrial process water, and as a corrosion-inhibiting aid in some systems.
- Textile and material treatment. As a cationic surfactant for antistatic and softening effects, and for microbial control on treated articles.
- Agriculture and horticulture. In some markets as an algaecide/microbiocide in irrigation and water systems.
Formulation: The Cationic Rule and Compatibility
DDAC’s cationic charge dominates its formulation behaviour. The single most important rule is that cationic quats are incompatible with anionic surfactants and anionic polymers: mixing them typically forms a precipitate or complex that deactivates both components.
| Component to consider | Behaviour with DDAC |
|---|---|
| Non-ionic surfactants | Compatible; commonly used together |
| Anionic surfactants (e.g. SLS, soaps) | Incompatible; precipitation and loss of activity |
| Cationic surfactants (e.g. other QACs) | Compatible |
| Strong oxidisers (e.g. hypochlorite) | Potential reaction; keep separate |
| Hard water / metal ions | Generally tolerated, but check performance |
Other practical formulation points: soil and organic matter consume the biocide, so cleaning before disinfection matters; DDAC is usually buffered to a near-neutral to slightly acidic pH; and blends with solvents and builders are designed to balance microbial kill, cleaning and corrosion behaviour.
DDAC vs Benzalkonium Chloride and Other Quats
DDAC competes and cooperates with other quaternary ammonium biocides. The table compares the most relevant ones.
| Quat | Structure | Notes |
|---|---|---|
| DDAC | Two C10 chains + two methyls | Strong biocide/algaecide; widely used in water treatment and sanitisers |
| BAC (benzalkonium chloride) | One C8–C18 chain (benzyl + methyls) | The classic disinfectant quat; broad use in healthcare and household products |
| DADMAC monomer/quat salts | Diallyl dimethyl ammonium | More a polymer/water-treatment coagulant chemistry than a biocide |
In practice DDAC and BAC are sometimes blended to broaden the antimicrobial spectrum and optimise cost, and both share the same cationic-compatibility rules. A fuller comparison of DDAC and BAC is given in the related reading below.
Safety, Health and Environment
- Skin and eye irritation. Concentrated DDAC solutions are corrosive/irritant to skin and eyes in the concentrated form; dilute use solutions are less aggressive but still require care. Use eye protection and gloves.
- Aquatic toxicity. Quats are toxic to aquatic life; prevent release to drains and watercourses.
- Handling. Avoid contact and inhalation of mists; work with adequate ventilation and follow the SDS.
- Storage. Keep sealed, cool and out of direct sunlight, in corrosion-resistant containers, away from anionic materials and oxidisers.
Regulatory Status
Biocides such as DDAC are heavily regulated because they are designed to kill organisms and are used in consumer products:
- Biocidal products. DDAC is an approved active substance for specific product types in markets such as the EU, and products must be authorised accordingly.
- End-use rules. The permitted uses (disinfectant, sanitiser, preservative, algaecide) and the maximum concentrations are set by the market and the application.
- Documentation. Buyers should obtain the SDS, COA and the applicable regulatory statements, and confirm that the grade and use are permitted in the target market.
Market and Supply Overview
- Demand drivers. Hygiene and disinfection, water treatment and material preservation; demand is broad and relatively stable.
- Production base. Made by a number of surfactant and biocide producers, mainly in Asia.
- Price drivers. The cost of the decylamine and decyl chloride feedstocks, and energy.
- Quality differentiators. Active content, residual amine, colour and clarity.
- Packaging. 200 kg drums and 1000 kg IBCs are typical for the 80% solution.
Procurement and Sourcing Guide
- Active content. Confirm the assay (80% standard) and the basis of the figure.
- Residual amine and pH. Check the free-amine limit and pH for your formulation.
- Grade and regulatory fit. Confirm the grade and documentation are acceptable for your use and market.
- Compatibility. Remember the cationic rule; avoid anionic actives in the same package.
- Packaging and storage. Confirm drum/IBC packaging and corrosion-resistant, cool, dark storage.
PolyBlueChem can supply DDAC 80% (CAS 7173-51-5). To request current specifications, a COA or a quotation, contact the PolyBlueChem team.
Building a QAC Disinfectant: Formulation Practice
A DDAC-based disinfectant is more than DDAC in water. A typical concentrate combines the active quat with a surfactant, a builder, a solvent and a pH buffer, and each component has a job.
| Component | Function | Typical chemistry |
|---|---|---|
| DDAC (or QAC blend) | Antimicrobial active | Didecyl dimethyl ammonium chloride |
| Non-ionic surfactant | Wetting, soil removal, synergy | Alcohol ethoxylates |
| Builder / chelant | Water softening, soil dispersion | Citrates, phosphonates, EDTA-type chelants |
| Solvent | Soil and grease removal | Glycol ethers, alcohols |
| pH buffer | Optimise stability and performance | Organic acid/salt systems |
Two design rules stand out. First, never pair the cationic quat with an anionic surfactant: the two neutralise each other, killing both detergency and antimicrobial activity. Second, remember that the biocide is consumed by soil, so a disinfectant must be used on a pre-cleaned surface at the label concentration and contact time. QAC disinfectants are usually supplied as concentrates that are diluted to the use concentration, and the dilution and contact time are specified to achieve the required log reduction of target organisms.
Water Treatment and Algaecide Applications
In water systems, DDAC acts as an algaecide and biocide, controlling the algae, bacteria and slime that foul cooling towers, recirculating systems, pools and industrial water.
- Cooling towers and recirculating water. Controls algae, bacteria and biofilm that reduce heat transfer and promote corrosion.
- Swimming pools and recreational water. Used as an algaecide in some markets, often with other sanitisers.
- Industrial process water. Controls microbial growth in pulp/paper, textile and other process waters.
- Oilfield water systems. Controls sulphate-reducing and other bacteria that cause souring and microbially influenced corrosion (MIC).
Because DDAC is cationic and works at surfaces, its efficacy depends on both concentration and contact, and dosing programmes are designed to maintain an effective residual. As with disinfectants, incompatibility with anionic chemicals (many scale inhibitors and dispersants are anionic) must be checked before products are combined in the same water system.
Wood Preservation and Material Protection
DDAC is used in wood preservation, where it protects timber against fungal decay and insect attack. It is often part of a multi-component preservative system, formulated with co-biocides and, in some systems, with copper, so that the treated timber is protected against the full range of organisms. Its cationic character helps it bind to the wood, improving retention and giving lasting protection. Beyond timber, DDAC-type quats are used to protect other materials — coatings, adhesives and technical products — against microbial spoilage.
Handling, Dilution and Storage
- Dilution. The 80% solution is diluted in water to the use concentration; use deionised or softened water where possible and add the concentrate to water under gentle agitation.
- Containers. Use corrosion-resistant (plastic or lined) containers; the cationic solution is generally compatible with plastic and stainless steel, but check.
- Avoid anionic contact. Never clean equipment that will hold DDAC with an anionic detergent residue; rinse thoroughly.
- PPE. Use eye protection and gloves, especially with the concentrate; avoid mist inhalation.
- Storage. Keep sealed, cool and out of direct sunlight, away from oxidisers, and rotate stock.
Why DDAC: A Practical Summary
Formulators and water-treatment engineers choose DDAC for a combination of reasons:
- Broad-spectrum, membrane-active kill. Effective against bacteria, fungi and algae, with a low tendency to induce target-specific resistance.
- High surface activity. The two long chains make it a potent biocide and surfactant at low active levels.
- Formulation flexibility. Compatible with non-ionic surfactants and solvents, so it builds into disinfectant and cleaning concentrates easily.
- Established regulatory pathway. As an approved biocide active in major markets, DDAC has a well-documented route to legal products, subject to the relevant authorisation.
The trade-off is the cationic rule: it cannot be combined with anionic materials, and it is toxic to aquatic life, so its use is managed with both formulation care and environmental responsibility.
Where DDAC Fits Among Biocide Actives
DDAC is one of several biocide chemistries, and knowing where it sits helps a formulator or water-treatment engineer choose and combine actives. The table contrasts the main classes.
| Biocide class | Examples | Strengths | Limitations |
|---|---|---|---|
| Quaternary ammonium (cationic) | DDAC, BAC | Broad-spectrum, residual activity, low odour, easy to formulate | Incompatible with anionics; consumed by soil; aquatic toxicity |
| Oxidising | Hypochlorite, peracetic acid, chlorine dioxide | Fast, powerful, no residue selectivity | Corrosive, short-lived, inactivated by organic matter |
| Non-oxidising, non-QAC | Isothiazolinones, glutaraldehyde, THPS | Effective at low dose; some used where QACs are not | Handling/toxicology issues; cost; compatibility |
Two practical patterns emerge. First, oxidising and non-oxidising biocides are often alternated or combined to prevent the build-up of resistant populations and to cover different parts of a system. Second, QACs such as DDAC are frequently chosen for their residual activity and formulation friendliness, and blended with other QACs to broaden the spectrum. Because DDAC is cationic, it is not combined with anionic scale inhibitors or dispersants in the same package.
DDAC Grades, Blends and Ready-to-Use Systems
- 80% active solution. The standard bulk grade for formulators, diluted to the use concentration on site.
- QAC blends. DDAC blended with BAC or other quats for a broader spectrum or tailored performance.
- Disinfectant and sanitiser concentrates. DDAC pre-formulated with surfactants, builders and solvents for dilution to a ready-to-use product.
- Water-treatment and algaecide formulations. DDAC as the active in products dosed into water systems.
Because these are all built from the same 80% bulk solution, the buyer’s decision is usually about active content, residual amine and documentation rather than about many distinct grades.
Frequently Asked Questions
What is DDAC and what is its CAS number?
DDAC is didecyl dimethyl ammonium chloride, a cationic quaternary ammonium biocide supplied as an 80% solution; its CAS number is 7173-51-5. See the product page for specifications.
What is the molecular formula of DDAC?
C22H48ClN, with a molecular weight of about 362.1 g/mol.
What is DDAC used for?
Mainly as a biocide and surfactant: disinfectants and sanitisers, water treatment (algaecide/biocide), wood preservation, oilfield and industrial water systems, and antimicrobial cleaning products.
Is DDAC the same as benzalkonium chloride?
No. They are different quaternary ammonium compounds: DDAC has two C10 chains; BAC has one alkyl chain plus a benzyl group. They are related and sometimes blended. See the comparison in the related reading.
Can DDAC be mixed with anionic surfactants?
No. As a cationic quat, DDAC is incompatible with anionic surfactants, which precipitate and deactivate it. Use non-ionic or cationic co-surfactants instead.
How is DDAC made?
By quaternisation of N,N-dimethyldecylamine with decyl chloride, then standardisation to the 80% solution.
Is DDAC hazardous?
Concentrated solutions are corrosive/irritant and toxic to aquatic life; dilution and appropriate PPE reduce the risk. Follow the SDS.
How should DDAC be stored?
Sealed, cool and out of direct sunlight, in corrosion-resistant containers, away from anionic materials and oxidisers.
References and Disclaimer
References. Substance identification data for didecyl dimethyl ammonium chloride (CAS 7173-51-5); standard chemistry of quaternary ammonium biocides and their membrane-disrupting antimicrobial mechanism; manufacturer technical data. Specifications quoted are representative and should be confirmed against the current certificate of analysis.
Disclaimer. This article is provided for general technical and commercial information only and does not constitute a specification or a warranty of fitness for any particular use. Users are responsible for confirming regulatory status, safe handling and suitability of the material for their own application and market.