Щавелевая кислота дигидрат чда

Химические свойства

white crystals

Использование

Oxalic acid dihydrate is a purifying agent in pharmaceutical industry, special in antibiotic medication, such as Oxytetracycline , Chloramphenicol , etc; * Precipitating agent in Rare-earth mineral processing; * Bleaching agent in the textile activities, wood pulp bleaching; * Rust-remover for Metal treatment; * Grinding agent, such as Marble polishing; * Waste water treatment, removing calcium from water.

Общее описание

Oxalic acid dihydrate (OAD) crystals are reported to be monoclinic with P2₁/n space group. The electron density of OAD has been obtained using X-ray diffraction studies under high resolution.

Профиль реактивности

At high temperatures oxalic acid decomposes, producing toxic carbon monoxide, andformic acid. Mixing with warm sulfuric acidmay produce the same products: CO2, CO,and formic acid. It reacts with many silvercompounds, forming explosive silver oxalate(NFPA 1986). An explosion occurred whenwater was added to an oxalic acid/sodiumchlorite mixture in a stainless steel beaker.There was also evolution of highly toxicchlorine dioxide gas (MCA 1962). Oxalicacid reacts violently with strong oxidizingsubstances.

Угроза здоровью

Oxalic acid is a strong poison. The toxicsymptoms from ingestion include vomiting, diarrhea, and severe gastrointestinaldisorder, renal damage, shock, convulsions,and coma. Death may result from cardiovascular collapse. The toxicity arises asoxalic acid reacts with calcium in the tissuesto form calcium oxalate, thereby upsettingthe calcium/potassium ratio (ACGIH 1986).Deposition of oxalates in the kidney tubulesmay result in kidney damage (Hodgson et al.1988).
Oxalic acid may be absorbed into the bodythrough skin contact. It is corrosive to theskin and eyes, producing burns. Dilute solutions of 10% strength may be a mild irritantto human skin. However, the inhalation toxicity is low because of its low vapor pressure.Airborne dusts can produce eyeburn and irritation of the respiratory tract.
LD50 value, oral (rats): 375 mg/kg.

Методы очистки

Crystallise oxalic acid from distilled water. Dry it in a vacuum over H2SO4. The anhydrous acid can be obtained by drying at 100o overnight. [Beilstein 2 IV 1819.]

Структура и конформация

The dihydrate H₂C₂O 4·2H₂O has space group C⁵_2h–P2_1/n, with lattice parameters a = 611.9 pm, b = 360.7 pm, c = 1205.7 pm, β = 106°19′, Z = 2. The main inter-atomic distances are: C-C 153 pm, C-O₁ 129 pm, C-O₂ 119 pm. In theory, oxalic acid dihydrate is one of the very few crystalline substances that exhibit negative area compressibility. Namely, when subjected to isotropic tension stress (negative pressure), the a and c lattice parameters increase as the stress decreases from -1.17? to -0.12 GPa and from -1.17 to -0.51 GPa, respectively.