Kiến thức

Carboxylic acid-Wikipedia

Carboxylic acid

From Wikipedia, the free encyclopedia

Jump to navigation

Jump to search

organic compound

Structure of a carboxylic acid

Carboxylate Anion

3D structure of a carboxylic acid

A carboxylic acid is an

organic acid

that contains a carboxyl group (C(=O)OH)

[1]

attached to an R-group. The general formula of a carboxylic acid is R−COOH or R−CO2H, with

R referring

to the

alkyl

,

alkenyl

,

aryl

, or other group. Carboxylic acids occur widely. Important examples include the

amino acids

and

fatty acids

. Deprotonation of a carboxylic acid gives a

carboxylate

anion

.

Examples and nomenclature[

edit

]

Carboxylic acids are commonly identified by their

trivial names

. They often have the suffix -ic acid.

IUPAC

-recommended names also exist; in this system, carboxylic acids have an -oic acid suffix.

[2]

For example,

butyric acid

(C3H7CO2H) is butanoic acid by IUPAC guidelines. For nomenclature of complex molecules containing a carboxylic acid, the carboxyl can be considered position one of the

parent chain

even if there are other

substituents

, such as

3-chloropropanoic acid

. Alternately, it can be named as a “carboxy” or “carboxylic acid” substituent on another parent structure, such as

2-carboxyfuran

.

The carboxylate anion (R–COO or RCO2) of a carboxylic acid is usually named with the suffix -ate, in keeping with the general pattern of -ic acid and -ate for a

conjugate acid

and its conjugate base, respectively. For example, the conjugate base of

acetic acid

is

acetate

.

Carbonic acid

, which occurs in

bicarbonate buffer systems

in nature, is not generally classed as one of the carboxylic acids, despite that it has a

moiety

that looks like a COOH group.

Straight-chain, saturated carboxylic acids (alkanoic acids)
Carbon
atoms
Common Name IUPAC Name Chemical formula Common location or use
1

Formic acid

Methanoic acid HCOOH

Insect stings

2

Acetic acid

Ethanoic acid CH3COOH

Vinegar

3

Propionic acid

Propanoic acid CH3CH2COOH Preservative for stored grains,

body odour

, milk, butter, cheese

4

Butyric acid

Butanoic acid CH3(CH2)2COOH

Butter

5

Valeric acid

Pentanoic acid CH3(CH2)3COOH

Valerian

plant

6

Caproic acid

Hexanoic acid CH3(CH2)4COOH

Goat

fat

7

Enanthic acid

Heptanoic acid CH3(CH2)5COOH Fragrance
8

Caprylic acid

Octanoic acid CH3(CH2)6COOH

Coconuts

9

Pelargonic acid

Nonanoic acid CH3(CH2)7COOH

Pelargonium

plant

10

Capric acid

Decanoic acid CH3(CH2)8COOH

Coconut

and

Palm kernel oil

11

Undecylic acid

Undecanoic acid CH3(CH2)9COOH Anti-fungal agent
12

Lauric acid

Dodecanoic acid CH3(CH2)10COOH

Coconut oil

and hand wash soaps

13

Tridecylic acid

Tridecanoic acid CH3(CH2)11COOH Plant metabolite
14

Myristic acid

Tetradecanoic acid CH3(CH2)12COOH

Nutmeg

15

Pentadecylic acid

Pentadecanoic acid CH3(CH2)13COOH Milk fat
16

Palmitic acid

Hexadecanoic acid CH3(CH2)14COOH

Palm oil

17

Margaric acid

Heptadecanoic acid CH3(CH2)15COOH Pheromone in various animals
18

Stearic acid

Octadecanoic acid CH3(CH2)16COOH

Chocolate

, waxes, soaps, and oils

19

Nonadecylic acid

Nonadecanoic acid CH3(CH2)17COOH Fats, vegetable oils,

pheromone

20

Arachidic acid

Icosanoic acid CH3(CH2)18COOH

Peanut oil

Other carboxylic acids
Compound class Members
unsaturated monocarboxylic acids

acrylic acid

(2-propenoic acid) – CH2=CHCOOH, used in polymer synthesis

Fatty acids

medium to long-chain saturated and unsaturated monocarboxylic acids, with even number of carbons, examples:

docosahexaenoic acid

and

eicosapentaenoic acid

(nutritional supplements)

Amino acids

the building-blocks of

proteins

Keto acids

acids of biochemical significance that contain a

ketone

group, examples:

acetoacetic acid

and

pyruvic acid

Aromatic

carboxylic acids

containing at least one aromatic ring, examples:

benzoic acid

– the sodium salt of benzoic acid is used as a food preservative,

salicylic acid

– a beta-hydroxy type found in many skin-care products,

phenyl alkanoic acids

– the class of compounds where a phenyl group is attached to a carboxylic acid

Dicarboxylic acids

containing two carboxyl groups, examples:

adipic acid

the monomer used to produce

nylon

and

aldaric acid

– a family of sugar acids

Tricarboxylic acids

containing three carboxyl groups, examples:

citric acid

– found in

citrus fruits

and

isocitric acid

Alpha hydroxy acids

containing a hydroxy group, examples:

glyceric acid

,

glycolic acid

and

lactic acid

(2-hydroxypropanoic acid) – found in sour milk,

tartaric acid

– found in wine

Divinylether fatty acids

containing a doubly unsaturated carbon chain attached via an ether bond to a fatty acid, found in some plants

Xem thêm: ĐLBT KHỐI LƯỢNG HÓA 8 THEO ĐHNL-Trường THCS Nguyễn Chí Thanh

Physical properties[

edit

]

Solubility[

edit

]

Carboxylic acids are

polar

. Because they are both hydrogen-bond acceptors (the carbonyl –C=O) and hydrogen-bond donors (the hydroxyl –OH), they also participate in

hydrogen bonding

. Together, the hydroxyl and carbonyl group form the functional group carboxyl. Carboxylic acids usually exist as dimers in nonpolar media due to their tendency to “self-associate”. Smaller carboxylic acids (1 to 5 carbons) are soluble in water, whereas bigger carboxylic acids have limited solubility due to the increasing hydrophobic nature of the alkyl chain. These longer chain acids tend to be soluble in less-polar solvents such as ethers and alcohols.

[3]

Aqueous sodium hydroxide and carboxylic acids, even hydrophobic ones, react to yield water-soluble sodium salts. For example,

enathic acid

has a low solubility in water (0.2 g/L), but its sodium salt is very soluble in water.

Solubility in different environments.jpg

Boiling points[

edit

]

Carboxylic acids tend to have higher boiling points than water, because of their greater surface areas and their tendency to form stabilised dimers through

hydrogen bonds

. For boiling to occur, either the dimer bonds must be broken or the entire dimer arrangement must be vaporised, increasing the

enthalpy of vaporization

requirements significantly.

Carboxylic acid

dimers

Acidity[

edit

]

Carboxylic acids are

Brønsted–Lowry acids

because they are proton (H+) donors. They are the most common type of

organic acid

.

Carboxylic acids are typically

weak acids

, meaning that they only partially

dissociate

into

H3O+

cations

and

RCOO

anions

in neutral

aqueous

solution. For example, at room temperature, in a 1-

molar

solution of

acetic acid

, only 0.4% of the acid are dissociated. Electron-withdrawing substituents, such as

-CF3 group

, give stronger acids (the pKa of formic acid is 3.75 whereas trifluoroacetic acid, with a

trifluoromethyl substituent

, has a pKa of 0.23). Electron-donating substituents give weaker acids (the pKa of formic acid is 3.75 whereas acetic acid, with a

methyl substituent

, has a pKa of 4.76)

Carboxylic acid

[4]

pKa

Acetic acid

(CH3CO2H)

4.76

Benzoic acid

(C6H5CO2H)

4.2

Formic acid

(HCOOH)

3.75

Chloroacetic acid

(CH2ClCO2H)

2.86

Dichloroacetic acid

(CHCl2CO2H)

1.29

Oxalic acid

(HO2CCO2H)

(first dissociation)

1.27

Oxalic acid

(HO2CCO2)

(second dissociation)

4.14

Trichloroacetic acid

(CCl3CO2H)

0.65

Trifluoroacetic acid

(CF3CO2H)

0.23

Deprotonation

of carboxylic acids gives carboxylate anions; these are

resonance stabilized

, because the negative charge is delocalized over the two oxygen atoms, increasing the stability of the anion. Each of the carbon–oxygen bonds in the carboxylate anion has a partial double-bond character. The carbonyl carbon’s partial positive charge is also weakened by the –1/2 negative charges on the 2 oxygen atoms.

Odour[

edit

]

Carboxylic acids often have strong sour odours.

Esters

of carboxylic acids tend to have pleasant odours, and many are used in

perfume

.

Characterization[

edit

]

Carboxylic acids are readily identified as such by

infrared spectroscopy

. They exhibit a sharp band associated with vibration of the C–O vibration bond (νC=O) between 1680 and 1725 cm−1. A characteristic νO–H band appears as a broad peak in the 2500 to 3000 cm−1 region.

[3]

By 1H

NMR

spectrometry, the

hydroxyl

hydrogen appears in the 10–13 ppm region, although it is often either broadened or not observed owing to exchange with traces of water.

Occurrence and applications[

edit

]

Many carboxylic acids are produced industrially on a large scale. They are also frequently found in nature. Esters of fatty acids are the main components of lipids and polyamides of

aminocarboxylic acids

are the main components of

proteins

.

Carboxylic acids are used in the production of polymers, pharmaceuticals, solvents, and food additives. Industrially important carboxylic acids include

acetic acid

(component of vinegar, precursor to solvents and coatings),

acrylic and methacrylic acids

(precursors to polymers, adhesives),

adipic acid

(polymers),

citric acid

(a flavor and preservative in food and beverages),

ethylenediaminetetraacetic acid

(chelating agent),

fatty acids

(coatings),

maleic acid

(polymers),

propionic acid

(food preservative),

terephthalic acid

(polymers). Important carboxylate salts are soaps.

Synthesis[

edit

]

Industrial routes[

edit

]

In general, industrial routes to carboxylic acids differ from those used on a smaller scale because they require specialized equipment.

  • Carbonylation of alcohols as illustrated by the

    Cativa process

    for the production of acetic acid. Formic acid is prepared by a different carbonylation pathway, also starting from methanol.

  • Oxidation of

    aldehydes

    with air using cobalt and manganese catalysts. The required aldehydes are readily obtained from alkenes by

    hydroformylation

    .

  • Oxidation of hydrocarbons using air. For simple alkanes, this method is inexpensive but not selective enough to be useful. Allylic and benzylic compounds undergo more selective oxidations. Alkyl groups on a benzene ring are oxidized to the carboxylic acid, regardless of its chain length.

    Benzoic acid

    from

    toluene

    ,

    terephthalic acid

    from para

    xylene

    , and

    phthalic acid

    from ortho

    xylene

    are illustrative large-scale conversions.

    Acrylic acid

    is generated from

    propene

    .

    [5]

  • Oxidation of ethene using

    silicotungstic acid

    catalyst.

  • Base-catalyzed dehydrogenation of alcohols.
  • Carbonylation coupled to the addition of water. This method is effective and versatile for alkenes that generate secondary and tertiary

    carbocations

    , e.g.

    isobutylene

    to

    pivalic acid

    . In the

    Koch reaction

    , the addition of water and carbon monoxide to alkenes is catalyzed by strong acids. Hydrocarboxylations involve the simultaneous addition of water and

    CO

    . Such reactions are sometimes called “

    Reppe chemistry

    .”

HCCH + CO + H2O → CH2=CHCO2H
  • Hydrolysis of

    triglycerides

    obtained from plant or animal oils. These methods of synthesizing some long-chain carboxylic acids are related to

    soap making

    .

  • Fermentation

    of ethanol. This method is used in the production of

    vinegar

    .

  • The

    Kolbe–Schmitt reaction

    provides a route to

    salicylic acid

    , precursor to

    aspirin

    .

Laboratory methods[

edit

]

Preparative methods for small scale reactions for research or for production of fine chemicals often employ expensive consumable reagents.

  • Oxidation of primary alcohols

    or

    aldehydes

    with strong

    oxidants

    such as

    potassium dichromate

    ,

    Jones reagent

    ,

    potassium permanganate

    , or

    sodium chlorite

    . The method is more suitable for laboratory conditions than the industrial use of air, which is “greener” because it yields less inorganic side products such as chromium or manganese oxides.[

    citation needed

    ]

  • Oxidative cleavage of

    olefins

    by

    ozonolysis

    ,

    potassium permanganate

    , or

    potassium dichromate

    .

  • Hydrolysis of

    nitriles

    ,

    esters

    , or

    amides

    , usually with acid- or base-catalysis.

  • Carbonation of a

    Grignard reagent

    and

    organolithium

    reagents:

RLi + CO2 → RCO2Li
RCO2Li + HCl → RCO2H + LiCl
  • Halogenation

    followed by hydrolysis of

    methyl ketones

    in the

    haloform reaction

  • Base-catalyzed cleavage of non-enolizable ketones, especially aryl ketones:

    [6]

RC(O)Ar + H2O → RCO2H + ArH

Less-common reactions[

edit

]

Many reactions produce carboxylic acids but are used only in specific cases or are mainly of academic interest.

  • Disproportionation of an

    aldehyde

    in the

    Cannizzaro reaction

  • Rearrangement of diketones in the

    benzilic acid rearrangement

    involving the generation of benzoic acids are the

    von Richter reaction

    from nitrobenzenes and the

    Kolbe–Schmitt reaction

    from

    phenols

    .

Xem thêm: Giáo án điện tử bài phương trình đường tròn lớp 10

Reactions[

edit

]

Carboxylic acid

organic reactions

The most widely practiced reactions convert carboxylic acids into esters, amides, carboxylate salts, acid chlorides, and alcohols. Carboxylic acids react with

bases

to form carboxylate salts, in which the hydrogen of the hydroxyl (–OH) group is replaced with a metal

cation

. For example, acetic acid found in vinegar reacts with

sodium bicarbonate

(baking soda) to form sodium acetate,

carbon dioxide

, and water:

CH3COOH + NaHCO3 → CH3COONa+ + CO2 + H2O

Carboxylic acids also react with

alcohols

to give

esters

. This process is widely used, e.g. in the production of

polyesters

. Likewise, carboxylic acids are converted into

amides

, but this conversion typically does not occur by direct reaction of the carboxylic acid and the amine. Instead esters are typical precursors to amides. The conversion of

amino acids

into

peptides

is a significant biochemical process that requires

ATP

.

The hydroxyl group on carboxylic acids may be replaced with a chlorine atom using

thionyl chloride

to give

acyl chlorides

. In nature, carboxylic acids are converted to

thioesters

.

Reduction[

edit

]

Like

esters

, most of carboxylic acid can be

reduced

to alcohols by

hydrogenation

or using hydride or alkyl transferring agents (since they will deprotonate the acids instead[

further explanation needed

] without transfer) such as

lithium aluminium hydride

or

Grignard reagents

(

organolithium

compounds).

N,N-Dimethyl(chloromethylene)ammonium chloride (ClHC=N+(CH3)2Cl) is a highly chemoselective agent for carboxylic acid reduction. It selectively activates the carboxylic acid to give the carboxymethyleneammonium salt, which can be reduced by a mild reductant like lithium tris(t-butoxy)aluminum hydride to afford an aldehyde in a one pot procedure. This procedure is known to tolerate reactive carbonyl functionalities such as ketone as well as moderately reactive ester, olefin, nitrile, and halide moieties.

[7]

Specialized reactions[

edit

]

  • As with all carbonyl compounds, the protons on the

    α-carbon

    are labile due to

    keto–enol tautomerization

    . Thus, the α-carbon is easily halogenated in the

    Hell–Volhard–Zelinsky halogenation

    .

  • The

    Schmidt reaction

    converts carboxylic acids to

    amines

    .

  • Carboxylic acids are decarboxylated in the

    Hunsdiecker reaction

    .

  • The

    Dakin–West reaction

    converts an amino acid to the corresponding amino ketone.

  • In the

    Barbier–Wieland degradation

    , an carboxylic acid on an aliphatic chain having a simple the

    methylene bridge

    at the alpha position can have the chain shortened by one carbon. The inverse procedure is the

    Arndt–Eistert synthesis

    , where an acid is converted into acyl halide, which is then reacted with

    diazomethane

    to give one additional methylene in the aliphatic chain.

  • Many acids undergo

    oxidative decarboxylation

    .

    Enzymes

    that catalyze these reactions are known as

    carboxylases

    (

    EC

     6.4.1) and

    decarboxylases

    (EC 4.1.1).

  • Carboxylic acids are reduced to

    aldehydes

    via the

    ester

    and

    DIBAL

    , via the acid chloride in the

    Rosenmund reduction

    and via the thioester in the

    Fukuyama reduction

    .

  • In

    ketonic decarboxylation

    carboxylic acids are converted to ketones.

  • Organolithium reagents (>2 equiv) react with carboxylic acids to give a dilithium 1,1-diolate, a stable

    tetrahedral intermediate

    which decomposes to give a ketone upon acidic workup.

  • The

    Kolbe electrolysis

    is an electrolytic, decarboxylative dimerization reaction. It gets rid of the carboxyl groups of two acid molecules, and joins the remaining fragments together.

Carboxyl radical[

edit

]

The carboxyl

radical

, •COOH, only exists briefly.

[8]

The

acid dissociation constant

of COOH has been measured using

electron paramagnetic resonance

spectroscopy.

[9]

The carboxyl group tends to dimerise to form

oxalic acid

.

Xem thêm: Tải file pdf 321 bài tập trắc nghiệm bất phương trình mũ và logarit

See also[

edit

]

  • Acid anhydride

  • Acid chloride

  • Amide

  • Amino acid

  • Ester

  • List of carboxylic acids

  • Dicarboxylic acid

  • Polyhydroxy carboxylic acid

    (PHC).

  • Pseudoacid

  • Thiocarboxy

References[

edit

]

  1. ^

    IUPAC

    ,

    Compendium of Chemical Terminology

    , 2nd ed. (the “Gold Book”) (1997). Online corrected version:  (2006–) “

    carboxylic acids

    “.

    doi

    :

    10.1351/goldbook.C00852

  2. ^

    Recommendations 1979

    . Organic Chemistry IUPAC Nomenclature. Rules C-4 Carboxylic Acids and Their Derivatives.

  3. ^

    a

    b

    Morrison, R.T.; Boyd, R.N. (1992). Organic Chemistry (6th ed.).

    ISBN

     

    0-13-643669-2

    .

  4. ^

    Haynes, William M., ed. (2011).

    CRC Handbook of Chemistry and Physics

    (92nd ed.).

    CRC Press

    . pp. 5–94 to 5–98.

    ISBN

     

    978-1439855119

    .

  5. ^

    Riemenschneider, Wilhelm (2002). “Carboxylic Acids, Aliphatic”. Ullmann’s Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH.

    doi

    :

    10.1002/14356007.a05_235

    .

    ISBN

     

    3527306730

    ..

  6. ^

    Perry C. Reeves (1977). “Carboxylation Of Aromatic Compounds: Ferrocenecarboxylic Acid”. Org. Synth. 56: 28.

    doi

    :

    10.15227/orgsyn.056.0028

    .

  7. ^

    Fujisawa, Tamotsu; Sato, Toshio.

    “Reduction of carboxylic acids to aldehydes: 6-Ooxdecanal”

    .

    Organic Syntheses

    . 66: 121.

    doi

    :

    10.15227/orgsyn.066.0121

    .; Collective Volume, 8, p. 498

  8. ^

    Milligan, D. E.; Jacox, M. E. (1971). “Infrared Spectrum and Structure of Intermediates in Reaction of OH with CO”. Journal of Chemical Physics. 54 (3): 927–942.

    Bibcode

    :

    1971JChPh..54..927M

    .

    doi

    :

    10.1063/1.1675022

    .

  9. ^

    The value is pKa = −0.2 ± 0.1. Jeevarajan, A. S.; Carmichael, I.; Fessenden, R. W. (1990). “ESR Measurement of the pKa of Carboxyl Radical and Ab Initio Calculation of the Carbon-13 Hyperfine Constant”. Journal of Physical Chemistry. 94 (4): 1372–1376.

    doi

    :

    10.1021/j100367a033

    .

External links[

edit

]

  • Carboxylic acids pH and titration

    – freeware for calculations, data analysis, simulation, and distribution diagram generation

  • PHC.

Retrieved from “

https://en.wikipedia.org/w/index.php?title=Carboxylic_acid&oldid=1024117740

Chuyên mục: Kiến thức

Related Articles

Trả lời

Email của bạn sẽ không được hiển thị công khai. Các trường bắt buộc được đánh dấu *

Back to top button