Carboxylic acid

Tshuaj organic compound, uas nws molecules muaj tsawg kawg yog ib tug carboxyl pab pawg neeg nyob rau hauv nws cov qauv (nws raws carbonyl - functional ib pawg ntawm aldehydes thiab ketones, thiab hydroxyl - cawv functional ib pawg) tau txais lub npe - carboxylic acid. Formula lawv yuav tuaj raws li R-COOH, qhov twg R yog ib tug monovalent hydrocarbon functional ib pawg. Tej carboxylic acid, nyob rau hauv sib piv rau feem ntau inorganic acids, tsis muaj zog thiab incompletely dissociated rau hauv ions.

Raws li qhov nyuaj piv txwv yog formic (methane) H-COOH acid. Lub npe yog hais txog mus rau lub keeb kwm ntawm lub thawj ntawm nws tau txais daim ntawv nyob rau hauv 1670 ntawm liab ntsaum English naturalist John Ray. Lub carboxylic acid muaj ob tug los yog ntau tshaj carboxyl pawg yuav tsum tau hu ua dibasic (dicarboxylic), tribasic (los yog tricarboxylic) thiab thiaj li nyob. Qhov yooj yim piv txwv yog oxalic acid thiab nws cov mis C2H2O4, nyob rau hauv lub molecule uas muaj ob carboxyl pawg. Raws li shestiosnovnoy yuav ua mellitic (geksakarbonovuyu) acid, nws mis C12H6O12. Cov qauv muaj rau carboxyl pawg yog hloov nyob rau hauv ib tug benzene hydrogen atoms nplhaib.

Organic acids feem ntau pom nyob rau hauv cov xwm. Piv txwv li, geksakarbonovaya acid muaj nyob rau hauv zib ntab pob zeb nyob rau hauv lignites).

Muaj ntau yam tseem ceeb ntuj tebchaw nyob rau hauv cov hoob kawm no. Cov no muaj xws citric acid C6H8O7 (nruab nrab ob peb zaub mov additives E330-E333), uas yog Ameslikas tau los ntawm cov unripe txiv qaub kua txiv nyob rau hauv 1784 los ntawm cov Swedish tus kws muab tshuaj K. Scheele. Tartaric acid C4H6O6 yog ib cov zaub mov additive E334). Qhov no carboxylic acid yog dav faib nyob rau hauv cov xwm. Nws yog muaj nyob rau hauv lub tshiab kua txiv ntawm ntau txiv hmab txiv ntoo.

Yog hais tias peb xav txog tej homologous series ntawm cov organic tebchaw, nyob rau hauv nws muaj kev hloov nyob rau hauv cov khoom nrog ua molecular ceeb thawj. Cov khoom ntawm txhua tus compound nyob ntawm seb cov qauv ntawm cov molecules, uas yog, nyob rau hauv ntau lub respects sij lawv isomerism carboxylic acids. Tus thawj cov neeg sawv cev ntawm lub homologous series tsim los ntawm formic acid, xws li acetic thiab propionic, yog hais txog mus rau ib tug kua. Lawv tsiag ntawv los ntawm ib tug pungent tsw thiab yog nkag soluble nyob rau hauv cov dej. Lub siab dua cov neeg sawv cev yog cov khib nyiab uas tsis yaj nyob rau hauv dej.

Tshuaj thaj chaw ntawm carboxylic acids mas txiav txim los ntawm tus ntawm cov carbonyl pab pawg neeg mus rau ib tug hydroxyl pab pawg neeg. Yog li ntawd, cov tebchaw, nyob rau hauv sib piv rau lub alcohols, muaj ib tug qhia tau acid cim.

Piv txwv li, nyob rau hauv aqueous lub ntsiab, tej zaum lawv yuav dissociate rau hauv ions, uas proves hais tias tus kua coloring tom qab ntxiv litmus liab. Qhov no qhia lub xub ntiag ntawm hydrogen cations. Hais tias yog, qhov nruab nrab ntawm lawv aqueous daws yog acidic (pH tsawg tshaj li 7).

Thaum interacting nrog co los yog bases muaj peev xwm ntawm txoj kev carboxylic acid ntsev: 2CH3-COOH + Mg → (CH3-hais nkwg) 2Mg + H2 ↑.

Organic acids kuj nkag rau hauv tshuaj tshua nrog carbonates, displacing carbonic acid: 2CH3-COOH + MgCO3 → (CH3-hais nkwg) 2Mg + H2O + CO2 ↑.

Lawv nkag hnov mob nrog ammonia tsim ntsev: CH3-COOH + NH3 → CH3-COONH4.

Lub acidic khoom no kho kom zoo thaum organic acids yog tam sim no nyob rau hauv lub radical nrog ib tug substituent tsis zoo inductive nyhuv. Piv txwv li, qhov kev txiav txim ntawm cov tshuaj nyob rau hauv acetic acid twb maj hloov ib hydrogen atom ntawm tshuaj atoms thiab tau txais chloroacetic acid, dichloroacetic acid, thiab ces trichloroacetic acid, muaj yog ib tug ntse nce nyob rau hauv lawv cov acidic zog.

Tej carboxylic acid yuav tsum tau nyob rau hauv ob peb txoj kev. Cov feem ntau yog txoj kev, uas yog raws li nyob rau hauv cov tshuaj tiv thaiv ntawm oxidation. Raws li cov thawj saib xyuas ntawm reactants alcohols los yog aldehydes. Lwm txoj kev ua organic acids yog lub hydrolysis ntawm nitriles ntws los ntawm cua sov lawv nrog diluted mineral acids.