Mosher's acid

Jump to: navigation, search
Mosher's acid
Mosher's acidMosher's acid
100px 100px
R and S MTPA
Systematic name (R/S)-3,3,3-trifluoro-2-
methoxy-2-phenylpropanoic acid
Other names Methoxytrifluorophenylaceticacid, MTPA
Molecular formula C10H9F3O3
SMILES COC(C(O)=O)(c1ccccc1)C(F)(F)F
Molar mass 234.17
Appearance ? solid
CAS number [20445-31-2](R), [17257-71-5](S),
[81655-41-6] racemic
Density and phase 1.303 g/mL, liquid
Solubility in water ? g/100 ml (?°C)
Melting point 46-49°C (? K)
Boiling point 105 - 107 °C 1 torr
Acidity (pKa) ?
Basicity (pKb) ?
Chiral rotation [α]D +73° (R) -73° (s)
Viscosity ? cP at ?°C
Dipole moment ? D
MSDS External MSDS
Main hazards ?
NFPA 704
Flash point 110°C
R/S statement R: R36/37/38
S: Template:S26-36
RTECS number ?
Supplementary data page
Structure and
n, εr, etc.
Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
Related compounds
Related ? Mosher's acid chloride
Related compounds ?
Except where noted otherwise, data are given for
materials in their standard state (at 25 °C, 100 kPa)
Infobox disclaimer and references

Mosher's acid, or α-methoxytrifluorophenylacetic acid is a carboxylic acid which was first by Harry S. Mosher used as a chiral derivitizing agent. It is a chiral molecule, consisting of R and S enantiomers.


As a chiral derivitizing agent, it reacts with an alcohol or amine of unknown stereochemistry to form an ester or amide. The configuration of the ester or amide is then determined by proton NMR spectroscopy.

Mosher's acid chloride, the acid chloride form, is sometimes used because it has better reactivity.


  • Y. Goldberg, H. Alper (1992). "A new and simple synthesis of Mosher's acid". Journal of Organic Chemistry. 57 (13): 3731–3732. doi:10.1021/jo00039a043.
  • J. A. Dale, D. L. Dull, H. S. Mosher (1969). "α-Methoxy-α-trifluoromethylphenylacetic acid, a versatile reagent for the determination of enantiomeric composition of alcohols and amines". Journal of Organic Chemistry. 34 (9): 2543–2549. doi:10.1021/jo01261a013.
  • D. L. Dull, H. S. Mosher (1967). "Aberrant rotatory dispersion curves of α-hydroxy- and α-methoxy-α-trifluoromethylphenylacetic acids". Journal of the American Chemical Society. 89 (16): 4230–4230. doi:10.1021/ja00992a053.
  • D. E. Ward, C. K. Rhee (1991). "A simple method for the microscale preparation of mosher's acid chloride". Tetrahedron Letters. 32 (49): 7165–7166. doi:10.1016/0040-4039(91)80466-J.
  • J. A. Dale, H. S. Mosher (1973). "Nuclear magnetic resonance enantiomer regents. Configurational correlations via nuclear magnetic resonance chemical shifts of diastereomeric mandelate, O-methylmandelate, and α-methoxy-α-trifluoromethylphenylacetate (MTPA) esters". Journal of the American Chemical Society. 95 (2): 512–519. doi:10.1021/ja00783a034.