Chlorinated paraffins (CPs) are complex mixtures of polychlorinated n-alkanes. The chlorination degree of CPs can vary between 30 and 70 wt%. CPs are subdivided according to their carbon chain length into short-chain CPs (SCCPs, C_10–13), medium-chain CPs (MCCPs, C_14–17) and long-chain CPs (LCCPs, C_>17). Depending on chain length and chlorine content, CPs are colorless or yellowish liquids or solids.

Production

Chlorinated paraffins are synthesized by reaction of

chlorine gas Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine is ...

with unbranched paraffin fractions (<2 % isoparaffins, <100 ppm aromatics) at a temperature of 80–100 °C. The radical substitution may be promoted by UV-light. : C_''x''H_(2''x''+2) + ''y'' Cl₂ → C_''x''H_{(2''x''−''y''+2)}Cl_''y'' + ''y'' HCl When the desired degree of chlorination is achieved, residues of

hydrochloric acid Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the dig ...

and chlorine are blown off with

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seve ...

. Epoxidized vegetable oil, glycidyl ether or organophosphorous compounds may be added to the final product for improved stability at high temperatures. Commercial products have been classified as substances of unknown or variable composition. CPs are complex mixtures of chlorinated n-alkanes containing thousands of homologues and

isomers In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. ...

which are not completely separated by standard analytical methods. CPs are produced in Europe, North America, Australia, Brazil, South Africa and Asia. In China, where most of the world production capacity is located, 600,000 tons of chlorinated paraffins were produced in 2007. Production and use volumes of CPs exceeded 1,000,000 tons in 2013.

Industrial applications

Production of CPs for industrial use started in the 1930s, with global production in 2000 being about 2 million tonnes. Currently, over 200 CP formulations are in use for a wide range of industrial applications, such as

flame retardant The term flame retardants subsumes a diverse group of chemicals that are added to manufactured materials, such as plastics and textiles, and surface finishes and coatings. Flame retardants are activated by the presence of an ignition source a ...

s and plasticisers, as additives in metal working fluids, in sealants, paints, adhesives, textiles, leather fat and coatings.

Safety

Short-chain CPs are classified as persistent and their physical properties ( octanol-water partition coefficient (logK_OW) 4.4–8, depending on the chlorination degree) imply a high potential for

bioaccumulation Bioaccumulation is the gradual accumulation of substances, such as pesticides or other chemicals, in an organism. Bioaccumulation occurs when an organism absorbs a substance at a rate faster than that at which the substance is lost or eliminated ...

. SCCPs are classified as toxic to aquatic organisms, and

carcinogenic A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive sub ...

to rats and mice. Therefore, it was concluded that SCCPs have PBT and vPvB properties and they were added to the Candidate List of

substances of very high concern A substance of very high concern (SVHC) is a chemical substance (or part of a group of chemical substances) concerning which it has been proposed that use within the European Union be subject to authorisation under the Registration, Evaluation, Au ...

for Authorisation under REACH Regulation. SCCPs (average chain length of C₁₂, chlorination degree 60 wt%) were categorised in group 2B as possibly carcinogenic to humans from the International Agency for Research on Cancer (IARC). In 2017, it was agreed to globally ban SCCPs under the

Stockholm Convention on Persistent Organic Pollutants Stockholm Convention on Persistent Organic Pollutants is an international environmental treaty, signed on 22 May 2001 in Stockholm and effective from 17 May 2004, that aims to eliminate or restrict the production and use of persistent organ ...

, effective December 2018. However, also MCCPs are toxic to the aquatic environment and persistent; MCCPs in soil, biota, and most of the sediment cores show increasing time trends over the last years to decades; MCCP concentrations in sediment close to local sources exceed toxicity thresholds such as the PNEC. In July 2021 also MCCPs were added to the Candidate List of Substances of Very High Concern (SVHC) under the REACH Regulation. Chlorinated paraffins have been detected in marine life such as

cetacean Cetacea (; , ) is an infraorder of aquatic mammals that includes whales, dolphins, and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively carnivorous diet. They propel them ...

s (whales) and

bivalve Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, biv ...

s (molluscs). Of particular concern is fetal accumulation in whales, with the chemicals beginning to build-up in the offspring before they are even born.

References

Sources

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External links

Short Chain Chlorinated Paraffins - Proposal for identification of a substance as a CMR, PBT, vPvB or a substance of an equivalent level of concern
{{Authority control Chloroalkanes Flame retardants IARC Group 2B carcinogens Soil contamination