Propyl 4-hydroxybenzoate

Structural formula
General
Surname	Propyl 4-hydroxybenzoate
other names	propyl p- hydroxybenzoate PHB propyl ester Propyl paraben Propyl 4-hydroxybenzoate ( IUPAC ) Propyl para- hydroxybenzoate E 216 (until 2006)
Molecular formula	C 10 H 12 O 3
Brief description	colorless, almost odorless, crystalline powder
External identifiers / databases
CAS number 94-13-3 EC number 202-307-7 ECHA InfoCard 100.002.098 PubChem 7175 DrugBank DB14177 Wikidata Q511627
properties
Molar mass	180.2 g · mol -1
Physical state	firmly
density	1.28 g cm −3 (20 ° C)
Melting point	95-98 ° C
boiling point	from 310 ° C
Vapor pressure	3.24 · 10 −2 Pa (50 ° C)
solubility	slightly soluble in water (0.4 g l −1 at 25 ° C) Methanol, ethanol, acetone, propylene glycol, diethyl ether
safety instructions
GHS labeling of hazardous substances no GHS pictograms H and P phrases H: no H-phrases P: no P-phrases
Toxicological data	6332 mg kg −1 ( LD 50 ,  mouse ,  oral )
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

4-hydroxybenzoate , and para -Hydroxybenzoesäurepropylester ( PHB propyl ester ), which is the propyl ester of aromatic carboxylic acid 4-hydroxybenzoic acid and one of the parabens .

properties

4-Hydroxybenzoic acid propyl ester is a colorless, odorless, crystalline substance that has a slightly burning taste and has a weak anesthetic effect. The melting point is 96.1 ° C with a melting enthalpy of 150.7 J · g ⁻¹ . The flash point is 180 ° C.

The compound crystallizes in a monoclinic crystal lattice with the space group P2 ₁ / c . The vapor pressure function results according to August according to ln (P) = −A / T + B (P in Pa, T in K) with A = 42.6 ± 0.2 and B = 14883 ± 77 in the temperature range from 46 ° C to 60 ° C. A molar enthalpy of sublimation of 123.7 kJ · mol ⁻¹ can be derived from the vapor pressure function . It does not dissolve very much in water (0.5 g / l at 25 ° C.), but it dissolves well in organic solvents such as acetone , chloroform , ethanol and ether . Phenolate ( sodium propyl p-hydroxybenzoate ) is formed in alkaline solutions .

Solubility in various solvents (at 25 ° C, in g / 100 g solvent)
solvent	water	Water (80 ° C)	Methanol	Ethanol	Propylene glycol	acetone	Diethyl ether	peanut oil
solubility	0.05	0.30	124	95	26th	105	50	1.5

The propyl 4-hydroxybenzoate forms eutectically melting mixtures with other 4-hydroxybenzoic acid esters .

Eutectics for mixtures of 4-hydroxybenzoic acid esters
	Methyl paraben	Ethyl paraben	Butyl paraben
Mole fraction of propyl paraben	0.65	0.60	0.33
Eutectic melting point	77.8 ° C	76.0 ° C	54.6 ° C

use

Propyl 4-hydroxybenzoate is a preservative for shampoos , shower gels and other cosmetic products , for example , in which it is considered safe in concentrations of up to 0.14% (when used individually or together with other PHB esters; calculated as an acid). It was also approved in the EU as a food additive with the number E 216 until 2006 . The sodium salt ( sodium propyl p- hydroxybenzoate , E 217 ) was usually used because of its better solubility .

After effects on sex hormones and the male reproductive system had been observed in experiments on rats and the EFSA was unable to set a safe maximum daily dose for humans, the EU prohibited its use in food in 2006. Since 2015, use in products that cannot be rinsed off ( leave-on preparations ) for use in the diaper area of ​​children under three years of age is no longer permitted.

Health hazards

Propyl 4-hydroxybenzoate was included by the EU in 2015 in accordance with Regulation (EC) No. 1907/2006 (REACH) as part of substance evaluation in the Community's ongoing action plan ( CoRAP ). The effects of the substance on human health and the environment are re-evaluated and, if necessary, follow-up measures are initiated. The ingestion of propyl 4-hydroxybenzoate was caused by concerns about consumer use , environmental exposure, exposure of sensitive population groups and widespread use, as well as the possible risk of reproductive toxicity and as a potential endocrine disruptor . The re-evaluation has been running since 2015 and is carried out by Belgium . In order to be able to reach a final assessment, further information was requested.

Individual evidence

1. ↑ ^{a b c} Entry on propyl 4-hydroxybenzoate in the GESTIS substance database of the IFA , accessed on July 9, 2016(JavaScript required) .
2. ↑ ^{a b c d e} Giordano, F .; Bettini, R .; Donini, C .; Gazzaniga, A .; Caira, MR; Zhang, GGZ; Grant, DJW: Physical properties of parabens and their mixtures: Solubility in water, thermal behavior, and crystal structures in J. Pharm. Sci. 88 (1999) 1210-1216, doi : 10.1021 / js9900452 .
3. ↑ ^{a b c d} data sheet Propyl 4-hydroxybenzoate from Sigma-Aldrich , accessed on May 9, 2017 ( PDF ).
4. ↑ ^{a b c} Perlovich, GL; Rodionov, SV; Bauer-Brandl, A .: Thermodynamics of solubility, sublimation and solvation processes of parabens in Eur. J. Pharm. Sci. 24 (2005) 25-33, doi : 10.1016 / j.ejps.2004.09.007 .
5. ↑ ^{a b} entry on 4-hydroxybenzoates. In: Römpp Online . Georg Thieme Verlag, accessed on July 10, 2016.
6. ↑ entry for propyl paraben in the ChemIDplus database of the United States National Library of Medicine (NLM), accessed on 8 December 2019 .
7. ↑ Data sheet n-Propyl 4-hydroxybenzoate from AlfaAesar, accessed on March 9, 2013 ( PDF )(JavaScript required) .
8. ↑ Directive 2006/52 / EC of the European Parliament and of the Council of July 5, 2006 amending Directive 95/2 / EC on food additives other than colors and sweeteners and Directive 94/35 / EC on sweeteners used in food allowed to. (PDF) Official Journal of the European Union, p. 13, 3. a) i), July 26, 2006.
9. ↑ Consumers: Commission improves the safety of cosmetics , press release of the European Commission, Brussels, 26 September 2014.
10. ↑ Community rolling action plan ( CoRAP ) of the European Chemicals Agency (ECHA): propyl 4-hydroxybenzoate , accessed on March 26, 2019.