Lactic acid

Catalog	BBC50215
CAS	50-21-5
Description	A concentrated solution of lactic acid is typically a mixture of lactic acid lactate and lactic acid. The concentration of this solution is approximately 90% (w/w). Lactic acid appears as a colorless to yellow odorless syrupy liquid. Corrosive to metals and tissue. Used to make cultured dairy products, as a food preservative, and to make chemicals. 2-hydroxypropanoic acid is a 2-hydroxy monocarboxylic acid that is propanoic acid in which one of the alpha-hydrogens is replaced by a hydroxy group. It has a role as a Daphnia magna metabolite and an algal metabolite. It is functionally related to a propionic acid. It is a conjugate acid of a lactate. A normal intermediate in the fermentation (oxidation, metabolism) of sugar. The concentrated form is used internally to prevent gastrointestinal fermentation. Sodium lactate is the sodium salt of lactic acid, and has a mild saline taste. It is produced by fermentation of a sugar source, such as corn or beets, and then, by neutralizing the resulting lactic acid to create a compound having the formula NaC3H5O3. Lactic acid was one of active ingredients in Phexxi, a non-hormonal contraceptive agent.
Synonyms	α-Hydroxypropanoic acid lactic acid 2-hydroxypropanoic acid DL-Lactic acid 50-21-5 2-hydroxypropionic acid
IUPAC Name	2-Hydroxypropanoic acid
Molecular Weight	90.08
Molecular Formula	C3H6O3
Canonical SMILES	CC(C(=O)O)O
InChI	InChI=1S/C3H6O3/c1-2(4)3(5)6/h2,4H,1H3,(H,5,6)
InChI Key	JVTAAEKCZFNVCJ-UHFFFAOYSA-N
Boiling Point	122 °C /15mmHg (lit.)
Melting Point	18 °C
Flash Point	>230 °F
Purity	98%
Density	1.209 g/ml
Solubility	Water-soluble
Appearance	Clear, water-white viscous liquid, characteristic odor
Application	Lactic acid appears as a colorless to yellow odorless syrupy liquid. Corrosive to metals and tissue. Used to make cultured dairy products, as a food preservative, and to make chemicals.Used as a solvent and acidulant in the production of foods, drugs, and dyes; Also used as a mordant in woolen goods printing, a soldering flux, a dehairing agent, and a catalyst for phenolic resins; Also used in leather tanning, oil well acidizing, and as a plant growth regulator. Applied in Petroleum Production and Refining, Soldering, Farming (Pesticides) ,Leather Tanning and Processing, Fur Dressing and Dyeing, Textiles (Printing, Dyeing, or Finishing) The fastest growing use for lactic acid is its use as a monomer for the production of polylactic acid or polylactide (PLA). Applications for PLA include containers for the food and beverage industries, films and rigid containers for packaging, and serviceware (cups, plates, utensils). The PLA polymer can also be spun into fibers and used in apparel, fiberfill (pillows, comforters), carpet, and nonwoven applications such as wipes. In dyeing baths, as mordant in printing woolen goods, solvent for water-insoluble dyes (alcohol-soluble induline, nigrosine, spirit-blue). Reducing chromates in mordanting wool. Manufacturing cheese, confectionery. Component of babies' milk formulas; acidulant in beverages; for acidulating worts in brewing. In preparation of sodium lactate injections. Ingredient of cosmetics. Component of spermatocidal jellies. For removing Clostridium butyricum in manufacturing of yeast; dehairing, plumping, and decalcifying hides. Solvent for cellulose formate. Flux for soft solder. Manufacturing lactates which are used in food products, in medicine, and as solvents. Plasticizer, catalyst in the casting of phenolaldehyde resins.
Storage	Store light-protected at a cool and dry place
EC Number	200-018-0
INCI Name	Lactic acid
pH	2
pKa	3.08
Refractive Index	n20/D 1.4262(lit.)
Solubility in Water	Soluble

Case Study

Lactic Acid as a Bio-Based Solvent for Promoting Green Multi-Component Reactions

Yang, Jie, Jia-Neng Tan, and Yanlong Gu. Green Chemistry 14.12 (2012): 3304-3317.

Lactic acid has emerged as a highly efficient, bio-based green solvent for promoting diverse organic transformations. In a recent study, it was employed for the first time to facilitate various three-component and condensation reactions, demonstrating its versatility in sustainable synthesis. These include (i) three-component reactions of styrenes, formaldehyde, and phenolic compounds or N,N-dialkylacetoacetamides, (ii) reactions involving diethyl acetylenedicarboxylate, anilines, and aromatic aldehydes, (iii) aniline-catalyzed condensations with salicylaldehydes, and (iv) Friedländer annulation to form substituted quinolines.
Among these, a representative procedure involved the reaction of formaldehyde, sesamol, and 4-methylstyrene in lactic acid at 100 °C, affording the desired product in 73% yield. Lactic acid enabled excellent solubility, reaction compatibility, and straightforward post-reaction work-up. Its recyclable nature and bio-derived origin underscore its alignment with green chemistry principles.
This application highlights lactic acid's significant potential as a green alternative to conventional organic solvents, offering superior synthetic efficiency and reduced environmental impact. Its ability to serve as both solvent and promoter in complex reaction environments reinforces its value in sustainable organic synthesis. The use of lactic acid in this context not only broadens the scope of green solvents but also contributes to the development of environmentally benign synthetic methodologies.

Lactic Acid-Derived Solvents Used for Eco-Friendly Varnish Removal in Canvas Painting Restoration

Melchiorre, Massimo, et al. Journal of Cultural Heritage 73 (2025): 206-214.

Lactic acid has recently proven valuable beyond synthetic chemistry, serving as a precursor for environmentally benign solvents in the restoration of cultural heritage artifacts. This study highlights the application of lactic acid-derived solvents-specifically 5-methyl-1,3-dioxolane-4-one (LA-H,H) and 2,2,5-trimethyl-1,3-dioxolane-4-one (LA-Me,Me)-in the removal of oxidized terpenoid varnishes from a 17th-century oil painting.
Traditionally, petroleum-based solvents like acetone and ethanol are used in restoration processes, posing health and environmental hazards. In contrast, the lactic acid-based solvents examined in this research are bio-based, biodegradable, and effective. LA-H,H, synthesized in multigram quantities and characterized by NMR and GC-MS, selectively removed dammar resin varnish without damaging the underlying paint layer. Ethyl lactate (EL), another lactic acid-derived solvent, also enabled complete varnish removal without residue.
Solvent properties were rationalized using Hansen solubility parameters and mapped via the Teas Triangle. Biodegradability was confirmed via OECD 301F testing, while TGA revealed evaporation behaviors favorable for restoration work.
This work underscores lactic acid's versatility as a platform chemical. Its derivatives offer high-performance, low-toxicity alternatives to traditional solvents in conservation science, aligning with sustainability goals and ensuring the safe preservation of irreplaceable cultural heritage.

Lactic Acid Is Used for the Electrodeposition of Ni-W-Se Coatings with Enhanced Hardness and Corrosion Resistance

Huang, Sheng-Jie, et al. Intermetallics 178 (2025): 108626.

Lactic acid plays a pivotal role in the electrodeposition of Ni-W-Se coatings by modulating the electrolyte chemistry and thereby influencing the composition, morphology, and performance of the deposited films. This study investigated the effect of lactic acid concentration (0.15-0.35 M) in combination with varying SeO₂ concentrations on the structural and functional characteristics of Ni-W-Se composite coatings.
The presence of lactic acid in the plating bath significantly affects phase formation. At lower concentrations (0.15-0.25 M), the coatings consist of elemental Ni and Se, along with WSe₂. Upon increasing the lactic acid concentration to 0.35 M, the formation of the NiSe intermetallic compound is favored at intermediate SeO₂ levels (0.4-0.5 g L⁻¹), while high SeO₂ concentrations suppress NiSe formation, reverting to Ni, Se, and WSe₂ phases.
Mechanical properties, particularly hardness, are closely tied to the W content, which is influenced by lactic acid-mediated complexation during deposition. The highest hardness (484.1 HV) was achieved at 0.25 M lactic acid and 0.6 g L⁻¹ SeO₂. Surface roughness and corrosion resistance were also lactic acid-dependent, with smoother surfaces and improved corrosion resistance observed at lower lactic acid concentrations. The best corrosion resistance (I_corr: 14.13 μA cm⁻²) was achieved under conditions with minimal Se content and smooth morphology.
This study confirms that lactic acid serves as a critical additive in optimizing the microstructure and performance of Ni-W-Se coatings through controlled electrodeposition.