Mosher's acid

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.

Mosher's acid

Names
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
Identifiers
CAS Number	(racemic): 81655-41-6 (R): 20445-31-2^[PubChem] (S): 17257-71-5^[PubChem]
3D model (JSmol)	Interactive image
ChemSpider	78043
ECHA InfoCard	100.153.604
EC Number	(R): 243-829-5 (S): 241-292-1
PubChem CID	(R): 2723917 (S): 6992788
UNII	(racemic): E015GCC0MA (R): 27O5L9T1WM (S): 172HCJ1IQV
CompTox Dashboard (EPA)	DTXSID90897007
InChI InChI=1S/C10H9F3O3/c1-16-9(8(14)15,10(11,12)13)7-5-3-2-4-6-7/h2-6H,1H3,(H,14,15) Key: JJYKJUXBWFATTE-UHFFFAOYSA-N InChI=1/C10H9F3O3/c1-16-9(8(14)15,10(11,12)13)7-5-3-2-4-6-7/h2-6H,1H3,(H,14,15) Key: JJYKJUXBWFATTE-UHFFFAOYAJ
SMILES COC(C(O)=O)(c1ccccc1)C(F)(F)F
Properties
Chemical formula	C10H9F3O3
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
Hazards
GHS pictograms
GHS Signal word	Warning
GHS hazard statements	H315, H319, H335
GHS precautionary statements	P261, P264, P271, P280, P302+352, P304+340, P305+351+338, P312, P321, P332+313, P337+313, P362, P403+233, P405, P501
Flash point	110 °C (230 °F; 383 K)
Related compounds
Related acyl chloride	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

Applications

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

• Pirkle's alcohol

References

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. 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.