para-Chloroaniline (PCA): Chemistry, Uses, Hazards and Textile Relevance

Para-chloroaniline (4-chloroaniline; CAS No. 106-47-8) is a substituted aromatic amine characterised by a chlorine atom in the para position on the aniline ring. It is principally used as an intermediate in the manufacture of dyes, pigments, agrochemicals and pharmaceuticals. NCBI+1 Given its potential formation as a by-product in textile dye manufacture, PCA has attracted regulatory and technical scrutiny in textile and finishing operations.

Chemical and Physical Properties

PCA is a pale yellow crystalline solid, slightly soluble in water and more soluble in organic solvents. It is produced mainly via reduction of p-nitrochlorobenzene. NCBI+1 It contains a primary amine group (–NH₂) and a para-chlorine substituent, which can influence its reactivity (for example in diazotisation or coupling reactions in dye synthesis).

Industrial Uses

• PCA is used as an intermediate in dye manufacture (for example as part of vat red intermediates, azoic coupling agents) and in pigment production. NCBI+1

• In the textile industry, it is not generally added directly to fabrics; rather, its relevance is as a potential impurity or cleavage product of certain azo/dye intermediates. StepChange Innovations Blog+1

Formation in Textile Context

In textile dyeing and finishing, the issue with PCA arises in these ways:

• Some azo dyes or reactive dyes (particularly those with chlorinated aromatic amine residues) may undergo reductive cleavage (for example under microbial, sweat or body-contact conditions) and release PCA or related amines. ScienceDirect+2Taylor & Francis Online+2

• During manufacture of the dye intermediates, inadequate purification may leave residual PCA or impurities that remain on the dye or fabric. StepChange Innovations Blog+1

• Effluent or sludge from textile dye-house operations may contain PCA or its derivatives, contributing to environmental release and occupational exposure. ResearchGate+1

Health and Environmental Hazards

• PCA is recognised as a hazardous aromatic amine. The International Programme on Chemical Safety (INCHEM) “CICADS 48” report notes toxicological concerns including effects on the liver, kidneys and blood system. InChem

• From a textile and chemical safety perspective, aromatic amines such as PCA are of concern because they may be released from dyed fabrics during wear or washing, leading to dermal exposure. SpringerLink+1

• Environmental fate: PCA has been shown to be persistent and recalcitrant in many wastewater and sludge contexts. A recent study indicates co-metabolic biodegradation of PCA by bacteria, but removal is incomplete. ScienceDirect+1

• Given its structural similarity to other known carcinogenic aromatic amines, regulatory regimes treat PCA with caution even where direct human epidemiological data may be limited.

Regulatory Framework and Textile Standards

• In the European Union: Azo dyes which, upon reductive cleavage, may release one or more of the regulated aromatic amines (which include PCA) at concentrations above 30 mg/kg are prohibited for use in textile and leather articles that are in direct and prolonged skin contact. SpringerLink+1

• Textile industry restricted substance lists (RSLs) and zero-discharge programmes often set acceptable residual PCA levels at 20–30 mg/kg (ppm) as practical control limits. StepChange Innovations Blog

• Analytical methods: The German standard method BGVV (1996) is noted for controlling PCA content in dyed textiles and paper. InChem

Implications for Textile Technology and Mill Practice

Given your background in textile production (preparatory winding, dyeing, continuous flow), here are practical points to consider:

• Dye selection: When procuring reactive or azo dyes, ensure supplier documentation that intermediate manufacture includes PCA-free or low-PCA routes.

• Process control: In dyeing/finishing operations with reactive/chlorinated dyes, monitoring of residual amine levels (pre- and post-soaping/rinsing) helps ensure compliance.

• Effluent/sludge management: Since PCA and related amines may persist in wastewater or sludge, ensure wastewater treatment systems (chemical/biological) are designed for aromatic amine removal — this ties in with your continuous production flow goals (minimising stoppages or secondary contamination).

• Analytical monitoring: Incorporate regular testing of finished textiles (especially those for direct skin contact) for PCA and other banned amines, using validated methods (GC/GC-MS, HPLC). NCBI+1

• Sustainability/risk mitigation: Shift where possible to dye chemistries designed for minimal amine-release (halogen-free, low-residuals) and invest in supplier audits, traceability, and certified dyes.

Research Gaps and Industry Challenges

• The toxicological profile of PCA in textile-wear-context (dermal release from finished garments over time) remains less quantified.

• Biodegradation and fate of PCA in textile-effluent systems: While recent studies show some removal, persistent fractions remain. ScienceDirect+1

• Cost and market-adoption barriers exist for fully PCA-free dye alternatives – as noted, some manufacturers still find market uptake limited unless buyer specification demands it. StepChange Innovations Blog

Conclusion

Para-chloroaniline occupies a pivotal role in dye chemistry and textile chemical safety. While it remains a valued intermediate in pigment and dye manufacture, its potential as a residual or cleavage product raises important compliance, process-control and sustainability considerations in the textile chain. For a textile technologist and production flow manager, aligning dye selection, process monitoring, analytical verification and effluent treatment around aromatic-amine risk (including PCA) is not just regulatory hygiene but supports continuous, safe operations and brand-risk reduction.

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References 

Carlsson, J., et al. (2022). Disperse azo dyes, arylamines and halogenated aromatic compounds in textiles: A review. [Journal Name], [Volume], [Pages].
Crettaz, S., et al. (2020). Survey on hazardous non-regulated aromatic amines as contaminants of textile dyes. Bundesgesundheitsblatt – Gesundheitsforschung – Gesundheitsschutz, 63, 54-66. https://doi.org/10.1007/s00003-019-01245-1 SpringerLink
De Mark, K. (2021). Comparative analysis of azo dye restriction in the US and Europe. AMPDUHT Working Paper, [Issue], 1-24. ScholarWorks
Edebali, O., et al. (2024). Tracking aromatic amines from sources to surface waters. Environmental Science & Technology Letters, 11(4), 273-281. https://doi.org/10.1021/acs.estlett.4c00032 American Chemical Society Publications
Hargesheimer, J., et al. (1981). Analytical methods for determination of aromatic amines including para-chloroaniline. [GC/FID method paper].
InChem (2003). 4-Chloroaniline (CICADS 48). Geneva: World Health Organization. InChem
M Zhu, et al. (2024). Biodegradation characteristics of p-Chloroaniline and the co-metabolism approach. Bioresource Technology, [Volume], [Pages]. ScienceDirect
Brüschweiler, B. J., & Merlot, M. (2017). Azo dyes in clothing textiles can be cleaved into a series of mutagenic aromatic amines. Regulatory Toxicology and Pharmacology, 88, 214-226. https://doi.org/10.1016/j.yrtph.2017.01.006 ScienceDirect
Step Change Innovations. (2025, July 15). Safer textiles: Phase out toxic and hazardous ingredients. Blog. StepChange Innovations Blog