(2R)-2-methoxypropanoic acid
[CAS 23943-96-6]

Identification

• Classification: Organic raw materials >> Carboxylic compounds and derivatives
• Name: (2R)-2-methoxypropanoic acid
• Molecular Formula: C₄H₈O₃
• Molecular Weight: 104.10
• CAS Registry Number: 23943-96-6
• EC Number: 809-116-3
• SMILES: C[C@H](C(=O)O)OC

Properties

• Density: 1.1±0.1 g/cm³ Calc.^*
• Boiling point: 199.4±13.0 °C 760 mmHg (Calc.)^*
• Flash point: 87.1±13.3 °C (Calc.)^*
• Index of refraction: 1.412 (Calc.)^*

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Safety Data

• Hazard Symbols: GHS05 Danger
• Risk Statements: H318
• Safety Statements: P264+P265-P280-P305+P354+P338-P317

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Serious eye damage	Eye Dam.	1	H318
Skin irritation	Skin Irrit.	2	H315
Specific target organ toxicity - single exposure	STOT SE	3	H335

chemBlink Chemical Story

A molecule with only four carbon atoms can illustrate two different kinds of chemical identity at once: how atoms are connected and how they are arranged in space. (2R)-2-Methoxypropanoic acid, CAS 23943-96-6, is a compact example. Its structure is CH₃CH(OCH₃)COOH, with a methoxy substituent beside a carboxylic acid group and a defined configuration at the intervening carbon.

The methoxy group is attached to carbon 2 through oxygen. It is not the methyl group of a methyl ester. This distinction is easy to overlook because methyl lactate, an ester of lactic acid, has the same formula, C₄H₈O₃. In methyl lactate the methyl group belongs to the carboxyl ester and the neighboring hydroxyl group remains free. In the present acid, the neighboring oxygen is methylated and the carboxyl group remains an acid. Equal molecular masses do not make these structures interchangeable.

Carbon 2 is bonded to four different groups: hydrogen, methyl, methoxy, and carboxyl. Its two mirror-image arrangements are enantiomers, and the R descriptor specifies one of them using the conventional sequence rules. This is a statement about absolute configuration. It does not, by itself, predict the direction in which a sample rotates plane-polarized light.

Supplier information identifies this particular enantiomer as the dextrorotatory product under stated measurement conditions. The plus sign and the R descriptor convey different information: one is an observed optical property, the other a structural assignment. Rotation also depends on measurement conditions, so a bare positive value without those conditions would be incomplete characterization.

The acid function offers a point for forming esters or amides, while the neighboring stereocenter makes preservation of configuration a separate synthetic concern. Describing that reactivity is not evidence that the molecule has a particular pharmaceutical effect. Nor should it be confused with more elaborate methoxy-substituted aromatic acids used in specialized stereochemical analyses simply because their names share a few words.

This compound's educational value lies in those distinctions. Constitutional identity separates it from an isomeric ester; absolute configuration separates it from its mirror image; and chemical purity is a different measurement from enantiomeric composition. A routine assay can establish how much material matches a chemical component without necessarily establishing the proportion of its two enantiomers. A useful specification therefore states which question each analytical result actually answers.

References:
1. Thermo Scientific Chemicals. (R)-(+)-2-Methoxypropionic acid, product AC331810010: identity and optical-rotation specification. https://www.fishersci.ca/shop/products/r-2-methoxypropionic-acid-97-thermo-scientific/AC331810010
2. PubChem. (2R)-2-methoxypropanoic acid, CID 2733584. https://pubchem.ncbi.nlm.nih.gov/compound/2733584