Mosher's acid

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Mosher's acid
(S)-Mosher Acid Formula V.1.svg
(R)-Mosher Acid Formula V.1.svg
IUPAC names
(R)-3,3,3-trifluoro-2-methoxy-2-phenylpropanoic acid
(S)-3,3,3-trifluoro-2-methoxy-2-phenylpropanoic acid
Other names
Methoxy(trifluoromethyl)phenylacetic acid, MTPA
3D model (JSmol)
ECHA InfoCard 100.153.604
Molar mass 234.17
Appearance solid
Melting point 46 to 49 °C (115 to 120 °F; 319 to 322 K)
Boiling point 105 to 107 °C (221 to 225 °F; 378 to 380 K) at 1 torr
R-phrases (outdated) R36/37/38
S-phrases (outdated) S26/S36
Flash point 110 °C (230 °F; 383 K)
Related compounds
Mosher's acid chloride
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

Mosher's acid, or α-methoxy-α-trifluoromethylphenylacetic acid (MTPA) is a carboxylic acid which was first used by Harry Stone Mosher as a chiral derivatizing agent.[1][2][3][4] It is a chiral molecule, consisting of R and S enantiomers.


As a chiral derivatizing agent, it reacts with an alcohol or amine[5] of unknown stereochemistry to form an ester or amide. The absolute configuration of the ester or amide is then determined by proton and/or 19F NMR spectroscopy.

Mosher's acid chloride, the acid chloride form, is sometimes used because it has better reactivity.[6]

See also[edit]


  1. ^ 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.
  2. ^ 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.
  3. ^ 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.
  4. ^ 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.
  5. ^ See for example: Mosher Amides: Determining the Absolute Stereochemistry of Optically-Active Amines Allen, Damian A.; Tomaso, Anthony E., Jr.; Priest, Owen P.; Hindson, David F.; Hurlburt, Jamie L. J. Chem. Educ. 2008, 85, 698. Abstract
  6. ^ 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.