Organophosphate esters & Physicochemical properties

Organophosphate esters

Organosphosphate esters (OPs) have been used since decades as flame retardants, plasticizers, anti-foaming agents and lubricants due to their technical characteristics. Lately, the worldwide restrictions on the use of polybrominated diphenyl ethers (first of the commercial mixtures of penta- and octa- BDE and more recently of deca-BDE as well) in new products, have led in the increased use of this type of flame retardants. For example, the annual consumption of OPFRs in EU increased from 84,000 tons in 2004 to 91,000 tons in 2006, with 56% of them being chlorinated phosphates. The fact that these numbers do not include the amount of alkyl phosphates used as plasticisers, shows that the overall consumption was much higher. The organosphosphate esters are additive flame retardants [1, 2].

Physicochemical properties

The variation observed in physicochemical properties of PFRs, depends more on the alcohol moieties esterified to the phosphoric acid. For example, in case of methyl group (TMP) the triester is very polar and volatile (logKow=-0.65, Vp=8*10-1 mm Hg), whereas with the large ehthylexyl groups (TEHP) it is very hydrophobic and non-volatile (logKow=9.5, Vp=8*10-8 mm Hg). That shows that the solubility in water generally decreases by increasing molecular mass. Most PFRs have a positive logKow value, which means they are more lipophilic than hydrophilic.

Vapor pressures and bioaccumulation factors (BCF) also vary among the PFRs. In general, the BCF increases by increasing the molecular mass, apart from compounds containing chlorine. Therefore, the PFRs with higher molecular masses are more likely to be found in the environment than those with lower molecular masses. Chlorine containing PFRs generally show no relation between the BCF and the molecular mass or the amount of chlorine in the molecule [3].

References:

1. A. Marklund Sundkvist, U. Olofsson. P. Haglund, “Organophosphorus flame retardants and plasticizers in marine and fresh water , biota and in human milk”, Journal of environmental monitoring, 2010, 12, p. 943 – 955, Available from: http://www.sciencedirect.com/ [Accessed: 20th October 2011]

2. N. van de Eede, A. C. Dirtu, H. Neels, A. Covaci, “Analytical developments and preliminary assessment of human exposure to organophosphate flame retardants from idoor dust”, Environment International, 37 (2011), p. 454 – 461, Available from: http://www.sciencedirect.com/ [Accessed: 12th March 2012]

3. T. Reetsma, J. Benito Quintana, R. Rodil, M. Garcia – Lopez, I. Rodriguez, “Organophosphorus flame retardants and plasticizers in water and air I. Occurrence and fate”, Trends in Analytical Chemistry, vol. 27, no. 9, 2008, p. 727 – 737, Available from: http://www.elsevier.com/ [Accessed: 15th March 2012]

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