Chloroacetaldehyde

Chloroacetaldehyde is an organic compound with the formula ClCH2CHO. Like some related compounds, it is highly electrophilic reagent and a potentially dangerous alkylating agent. The compound is not normally encountered in the anhydrous form, but rather as the hemiacetal (ClCH2CH(OH))2O.

Chloroacetaldehyde
Structural formula
Ball-and-stick model
Names
Preferred IUPAC name
Chloroacetaldehyde
Systematic IUPAC name
Chloroethanal
Other names
2-Chloroacetaldehyde
2-Chloroethanal
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.003.158
EC Number
  • 203-472-8
UNII
Properties
C2H3ClO
Molar mass 78.50 g mol−1
Appearance Colourless liquid
Odor acrid, penetrating[1]
Density 1.117 g/mL
Melting point −16.3 °C (2.7 °F; 256.8 K)
Boiling point 85 to 85.5 °C (185.0 to 185.9 °F; 358.1 to 358.6 K)
soluble[1]
Solubility organic solvents
Hazards
Main hazards alkylating agent
Flash point 87.7 °C (189.9 °F) (closed cup)
Lethal dose or concentration (LD, LC):
89 mg/kg (oral, rat)
82 mg/kg (oral, mouse)[2]
200 ppm (rat, 1 hr)[3]
NIOSH (US health exposure limits):
PEL (Permissible)
 C 1 ppm (3 mg/m3)[4]
REL (Recommended)
 C 1 ppm (3 mg/m3)[4]
IDLH (Immediate danger)
 45 ppm[4]
Related compounds
Related compounds
 2-chloroethanol, Chloroacetic acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Chloroacetaldehyde is a useful intermediate in the synthesis of 2-aminothiazole[1] including the pharmaceuticals altizide, polythiazide, brotizolam and ciclotizolam.[5] Another use is to facilitate bark removal from tree trunks.[1]

Synthesis and reactions

Hydrated chloroacetaldehyde is produced by the chlorination of aqueous vinyl chloride:

ClCH=CH2 + Cl2 + H2O → ClCH2CHO + 2 HCl

It can also be prepared from vinyl acetate[6] or by careful chlorination of acetaldehyde.[1] The related bromoacetaldehyde is prepared via bromination of vinyl acetate. It also rapidly forms an acetals in the presence of alcohols.[7]

Being bifunctional, chloroacetaldehyde is a versatile precursor to many heterocyclic compounds. It condenses with thiourea derivatives to give aminothiazoles. This reaction was important as a precursor to sulfathiazole, one of the first sulfa drugs.[6]

Anhydrous

Water free chloroacetaldehyde is prepared from the hydrate by azeotropic distillation with chloroform, toluene or carbon tetrachloride. Anhydrous chloroacetaldehyde reversibly converts to polyacetals.[5][1] Less reactive chloroacetaldehyde derivatives might be used instead to obtain chloroacetaldehyde or bypass its intermediate formation completely: e.g. chloroacetaldehyde dimethyl acetal (2-chloro-1,1-dimethoxyethane) hydrolyzes in acidic conditions to give chloroacetaldehyde, which may then quickly react with the other reagents[5] instead of polymerizing.

Hemihydrate

Hemihydrate is formed as below. It has a melting point of 43–50°C, boiling point of 85.5 °C.[1]

Environmental aspects

Chloroacetaldehyde is a metabolite in the degradation of 1,2-dichloroethane, which initially converts to chloroethanol. This metabolic pathway is topical because 1,2-dichloroethane is produced on a large as a precursor to vinyl chloride.[8]

Safety

Chloroacetaldehyde is corrosive to mucous membranes. It irritates eyes, skin and respiratory tract.[1]

Based on data collected from human studies in 1962, exposures to 45 ppm of chloroacetaldehyde were found to be disagreeable and caused conjunctival irritation to the subjects.[9] The Occupational Safety and Health Administration established a permissible exposure limit at a ceiling of 1 ppm (3 mg/m3) for exposures to chloroacetaldehyde.[10]

References
  1. The Merck index. S Budavari, M O'Neil, A Smith (12 ed.). Merck. 1996. p. 2108. ISBN 9780911910124.CS1 maint: others (link)
  2. "Chloroacetaldehyde". National Institute for Occupational Safety and Health. 4 December 2014. Retrieved 20 February 2015.
  3. "Chloroacetaldehyde". Immediately Dangerous to Life and Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  4. NIOSH Pocket Guide to Chemical Hazards. "#0118". National Institute for Occupational Safety and Health (NIOSH).
  5. Keiji, T (1992-10-30). "α-Chlorocarbonyl Compounds: Their Synthesis and Applications (Commemoration Issue Dedicated to Professor Shigeo Tanimoto On the Occation of His Retirement)". Bulletin of the Institute for Chemical Research, Kyoto University. 70 (3): 341. hdl:2433/77455. ISSN 0023-6071.
  6. Jira, Reinhard; Kopp, Erwin; McKusick, Blaine C.; Röderer, Gerhard; Bosch, Axel; Fleischmann, Gerald (2007). "Chloroacetaldehydes". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a06_527.pub2.
  7. S. M. McElvain and D. Kundiger "Bromoacetal" Organic Syntheses 1943, volume 23, p. 8. doi:10.15227/orgsyn.023.0008.
  8. Janssen, D. B.; van der Ploeg, J. R. and Pries, F., "Genetics and Biochemistry of 1,2-Dichloroethane Degradation", Biodegradation, 1994, 5, 249-57.doi:10.1007/BF00696463
  9. Documentation for Immediately Dangerous To Life or Health Concentrations (IDLHs)
  10. CDC - NIOSH Pocket Guide to Chemical Hazards
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