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Commercial nomenclature for the ester formed by condensation of phthalic anhydride with two molar equivalents of n-butanol is rarely uniform across regulatory, analytical, and polymer-processing documents. The substance is registered as 84-74-2 under Chemical Abstracts Service, assigned the European inventory number 201-557-4, and indexed in the CLP Annex VI as 607-318-00-4. The same compound appears in older lacquer and plastisol literature as di-n-butyl phthalate, 1,2-benzenedicarboxylic acid dibutyl ester, phthalic acid dibutyl ester, o-benzenedicarboxylic acid dibutyl ester, and simply DBP. The multiplicity of names arises because the parent acid can be expressed as phthalic acid, benzene-1,2-dicarboxylic acid, or o-benzenedicarboxylic acid, while the alkyl substituent can be described as dibutyl, di-n-butyl, or butyl. This variability does not affect the CAS registration, but it does create practical confusion in Safety Data Sheets, import declarations, analytical certificates, and restricted-substance databases. The abbreviation DBP also has a separate technical meaning as dibutyl phosphate in organophosphate and solvent-extraction chemistry, which is assigned CAS 107-66-4 and is chemically distinct from the phthalate ester. Consequently, industrial and analytical records should always pair the abbreviation with the CAS Registry Number when the intended substance is dibutyl phthalate.
The preferred IUPAC name dibutyl benzene-1,2-dicarboxylate orders the alcohol-derived alkyl groups before the parent benzene ring and specifies the carboxylate positions at the 1,2-locations. The CAS index name, by contrast, treats the substance as a benzenedicarboxylic acid derivative and lists the ester substituents after the parent acid, generating 1,2-benzenedicarboxylic acid, 1,2-dibutyl ester. Some secondary sources shorten the CAS index name to 1,2-benzenedicarboxylic acid, dibutyl ester, but the underlying registry number remains 84-74-2. Both index names describe the same molecular formula C16H22O4 and the same molar mass of 278.34 g/mol. The linear structural encoding is CCCCOC(=O)c1ccccc1C(=O)OCCCC, corresponding to two n-butyl ester groups attached to the ortho positions of an aromatic ring. The InChIKey for this substance is DOIRQSBPKHKJHM-UHFFFAOYSA-N, and the record contains no stereochemical markers because the n-butyl side chains are unbranched. The assignment of CAS 84-74-2 is independent of synthesis route, distillation cut, plasticizer trade designation, or minor technical-grade impurities; it identifies the defined diester formed from phthalic acid and n-butanol. Information systems that map synonyms to CAS numbers must therefore recognise that phthalic acid dibutyl ester, benzene-o-dicarboxylic acid dibutyl ester, and di-n-butyl phthalate are the same registry entity, while diisobutyl phthalate is a separate entity with its own registry assignment.
The following identifiers form the cross-reference needed for industrial hygiene, customs classification, environmental reporting, and analytical data management. The identifiers are not interchangeable in scope. The EC number identifies the substance in the European EINECS inventory, the CLP Annex VI Index number links to harmonised classification and labelling, and the RTECS number indexes toxicological literature. The UN number applies only when the material is shipped as an environmentally hazardous substance under transport regulations. The table summarises the core identity record for dibutyl phthalate.
| Identifier or property | Value | Source or framework |
|---|---|---|
| CAS Registry Number | 84-74-2 | Chemical Abstracts Service |
| CAS Index Name | 1,2-Benzenedicarboxylic acid, 1,2-dibutyl ester | Chemical Abstracts Service |
| Preferred IUPAC Name | Dibutyl benzene-1,2-dicarboxylate | IUPAC |
| EC Number | 201-557-4 | EINECS |
| CLP Annex VI Index Number | 607-318-00-4 | Regulation (EC) No 1272/2008 |
| Molecular formula | C16H22O4 | — |
| Molar mass | 278.34 g/mol | — |
| Canonical SMILES | CCCCOC(=O)c1ccccc1C(=O)OCCCC | — |
| InChIKey | DOIRQSBPKHKJHM-UHFFFAOYSA-N | IUPAC InChI |
| RTECS Number | TI0875000 | NIOSH RTECS |
| UN Number | UN 3082; Class 9, Packing Group III | UN Model Regulations |
In European regulatory submissions under REACH, the EC number and CAS Registry Number are used together because the CAS number alone may be insufficient to locate the correct CLP Annex VI entry in older databases. For DBP, the harmonised classification is attached to Index number 607-318-00-4, and this number is legally required in Section 1.1 of a European Safety Data Sheet when the substance or mixture is classified as hazardous. The RTECS number TI0875000 is not a regulatory identifier, but it is a useful retrieval key for toxicological studies. The transport designation UN 3082 is assigned only after the shipper evaluates the aquatic toxicity criterion; because DBP is classified Aquatic Acute 1 with hazard statement H400, it commonly meets the threshold for transport as an environmentally hazardous substance, liquid, n.o.s. (dibutyl phthalate) in Class 9, Packing Group III. Under the IMDG Code, the substance is also considered a marine pollutant, and the transport document must show the correct technical name in parentheses. These transport identifiers are not chemical synonyms; they are hazard-based classifications attached to the same chemical identity.
Synonyms cannot be treated as separate substances. In flexible PVC compounding and nitrocellulose lacquer formulations, historical records may refer to the plasticizer as di-n-butyl phthalate, butyl phthalate, or simply DBP. The name o-benzenedicarboxylic acid dibutyl ester derives from the ortho relationship of the two ester groups. Trade designations reported in polymer-processing and plasticizer distribution literature include Palatinol C, Vestinol C, Unimoll DB, Polycizer DBP, Staflex DBP, Reomol DBP, and Morflex DBP. These trade designations may cover material assigned to CAS 84-74-2 but can differ in purity specification, trace phthalate profile, moisture content, colour as APHA, or packaged stabilizer content. A Safety Data Sheet should therefore list the CAS Registry Number 84-74-2 and the EC number 201-557-4 alongside the supplier trade designation. The abbreviation DBP itself is ambiguous outside the plasticizer, coatings, and rubber industries. In solvent extraction, nuclear fuel reprocessing, and phosphate chemistry, DBP also denotes dibutyl phosphate, CAS 107-66-4, a distinct organophosphorus compound with markedly different toxicological and reactivity profiles. A process record describing a 25% by volume solution of DBP in tributyl phosphate refers to dibutyl phosphate, not dibutyl phthalate. The ambiguity is resolved only by pairing the abbreviation with the correct CAS number. Databases should therefore store the preferred chemical name, the IUPAC name, and any trade designation as metadata attached to the unique registry number, never as a standalone abbreviation.
Under REACH, dibutyl phthalate is included in the Candidate List as a substance of very high concern under Article 57(c) for reproductive toxicity and under Article 57(f) for endocrine-disrupting properties with probable serious effects to human health and the environment. Its presence on the REACH Annex XIV authorisation list means that placing on the market or use in the European Economic Area after the relevant sunset date requires an authorisation for any non-exempt application. The restriction regime operates separately. REACH Annex XVII entry 51 restricts DBP in toys and childcare articles, where the total concentration of DBP, diisobutyl phthalate, benzyl butyl phthalate, and bis(2-ethylhexyl) phthalate must not exceed 0.1% by weight of the plasticised material. In electrical and electronic equipment, DBP is one of four phthalates restricted under Annex II of the RoHS Directive 2011/65/EU, as added by Commission Delegated Directive (EU) 2015/863, with a maximum concentration of 0.1% by weight in homogeneous materials. The harmonised classification in CLP Annex VI for CAS 84-74-2 is reproductive toxicity category 1B with hazard statement H360Df and aquatic acute category 1 with hazard statement H400. The same Index number 607-318-00-4 is used in SCIP notifications under the Waste Framework Directive when an article contains DBP above 0.1% by weight. In the United States, DBP appears on the California Proposition 65 list as a substance known to cause reproductive toxicity, which triggers state-level warning and testing obligations for certain product categories. These regulatory entries are anchored to the CAS Registry Number and EC number, not to a trade name; a plasticizer marketed as Palatinol C or Vestinol C remains the regulated substance DBP and must be reported accordingly.
Analytical confirmation of DBP identity in a supplier certificate of analysis should not rely on total phthalate content alone. Gas chromatographic or gas chromatographic-mass spectrometric methods for ortho-phthalate esters typically monitor the phthalic anhydride fragment at m/z 149; for DBP, additional fragments from the loss of C4H9 and C4H9O groups appear in the full spectrum, but the same fragments are produced by diisobutyl phthalate. A capillary column with a 5%-phenyl–95%-dimethylpolysiloxane stationary phase and dimensions of 30 m × 0.25 mm × 0.25 μm may not resolve DBP from DIBP under a rapid temperature program. A midpolarity column or a slowed ramp from 120 °C to 300 °C at 10 °C/min is often required to separate the two esters. Standard methods such as EPA Method 8061A and ISO 18856 provide extraction, clean-up, and chromatographic validation procedures for selected phthalate esters. In production-scale plasticizer quality control, gas chromatography with flame ionisation detection is used for assay, and the retention time is bracketed against a certified reference material of CAS 84-74-2. The result is reported as dibutyl phthalate or di-n-butyl phthalate, not as DBP, to avoid confusion with dibutyl phosphate. Liquid chromatography with ultraviolet detection at 224 nm may be used as an alternative technique when direct gas chromatographic injection of raw plasticizer causes inlet contamination, but retention-time confirmation against the certified standard remains mandatory.
Registry-level confusion between dibutyl phthalate and diisobutyl phthalate creates a distinct analytical and regulatory hazard. Diisobutyl phthalate is CAS 84-69-5, not CAS 84-74-2, and its chemical name is 1,2-benzenedicarboxylic acid, 1,2-bis(2-methylpropyl) ester. Both substances share the molecular formula C16H22O4 and the molar mass 278.34 g/mol, so molecular weight alone cannot differentiate them. The structural difference lies in the branching of the alkyl chains: DBP contains two n-butyl groups, O–CH2–CH2–CH2–CH3, while DIBP contains two 2-methylpropyl groups, O–CH2–CH(CH3)2. This difference alters retention time, boiling range, viscosity, and regulatory status. Under RoHS and REACH Annex XVII entry 51, both substances are counted together with benzyl butyl phthalate and bis(2-ethylhexyl) phthalate in the total phthalate calculation. A method that misidentifies DIBP as DBP or fails to integrate the correct chromatographic peak can produce an incorrect total phthalate report. In gas chromatographic analysis of plasticised PVC, DBP and DIBP are among the most difficult isomeric pairs to separate because their mass spectra are nearly identical and both produce the m/z 149 base peak. Confirmation therefore requires analysis of both the submitted sample and a mixed certified reference material containing DBP, DIBP, BBP, and DEHP, with retention-time windows narrow enough to prevent cross-assignment but wide enough to account for matrix-induced retention time shifts. Di-sec-butyl phthalate and di-tert-butyl phthalate represent additional isomeric butyl phthalates with separate registry numbers, but published data for their use in plasticizer applications is limited relative to DBP and DIBP.
Commercial DBP for plasticizer and coatings applications is produced by esterification of phthalic anhydride with n-butanol. The condensation is carried out under acid catalysis; the water of reaction is removed azeotropically, and the crude ester is neutralised, washed, steam-stripped, and vacuum-distilled. Typical technical-grade specifications include an ester content by gas chromatography of not less than 99.0%, an acid value not exceeding 0.10 mg KOH/g, a moisture content not exceeding 0.10% by mass, and a colour on the platinum-cobalt scale not exceeding 20 APHA. These limits are not universal; they vary among producers and applications, and the exact specification for a given batch should appear on the certificate of analysis. The relationship between purity and nomenclature is practical: a batch labelled DBP may contain traces of monobutyl phthalate and residual n-butanol, but the dried diester fraction is assigned to CAS 84-74-2. In quality systems, incoming raw material is therefore recorded with the CAS Registry Number 84-74-2, the EC number 201-557-4, and the supplier trade designation, ensuring that chemical identity remains traceable from bulk storage through dispensing, compounding, and final article testing.
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