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From Wikipedia

Acetate

Acetate is a derivative of acetic acid. Two types of derivatives are known, salts and ester. Most of the approximately 5 billion kilograms of acetic acid produced annually in industry are acetates, which usually take the form of polymers. In nature, acetate is the most common building block for biosynthesis. For example, the fatty acids are produced by connecting C2 units derived from acetate.

Nomenclature and presentation of formula

When part of a salt, the formula of the acetate anion is written as CH3CO2−, C2H3O2−, and CH3COO−. Chemists abbreviate acetate as OAc− and AcO−. Thus, HOAc is the abbreviation for acetic acid, NaOAc for sodium acetate, and EtOAc for ethyl acetate.

The name for acetate, sanctioned by IUPAC, the international committee charged with naming chemical compounds, is ethanoate. This term is rarely encountered.

Salts

The acetate anion, [CH3COO]−, is one of the carboxylate family. It is the conjugate base of acetic acid. Above pH of 5.5, acetic acid converts to acetate:

CH3COOH CH3COO− + H+

Many acetate salts are ionic, indicated by their tendency to dissolve well in water. A commonly encountered acetate in the home is sodium acetate, a white solid that can be prepared by combining vinegar and sodium bicarbonate ("bicarb"):

CH3COOH + NaHCO3→ CH3COO−Na+ + H2O + CO2

More specialized metal acetates can have complicated structures. Acetate is a relatively strong ligand in coordination chemistry. Examples of acetate complexes include chromium(II) acetate and basic zinc acetate.

Applications

Commercially important acetate salts are aluminium acetate, used in dyeing, ammonium acetate, a precursor to acetamide, and potassium acetate, used as a diuretic. All three salts are colourless and highly soluble in water.

Esters

Acetate esters have the general formula CH3CO2R, where R is an organyl group. The esters are the dominant forms of acetate in the marketplace. Unlike the acetate salts, acetate esters are often liquids, lipophilic, and sometimes volatile. They are popular because they have inoffensive, often sweet odors, they are inexpensive, and they are usually of low toxicity.

Applications

Almost half of acetic acid production is consumed in the production of vinyl acetate, precursor to polyvinyl alcohol, which is a component of many paints. The second largest use of acetic acid is consumed in the production of cellulose acetate. In fact, "acetate" is jargon for cellulose acetate, which is used in the production of fibres or diverse products, e.g. the acetate discs used in audio record production. Cellulose acetate can be found in many household products. Many industrial solvents are acetates, including methyl acetate, ethyl acetate, isopropyl acetate, ethylhexyl acetate. Butyl acetate is a fragrance used in food products.

Acetate in biology

Acetate is a common anion in biology. It is mainly utilized by organisms in the form of acetyl coenzyme A.

Intraperitoneal injection of sodium acetate (20 or 60 mg per kg body mass) was found to induce headache in sensitized rats, and it has been proposed that acetate resulting from oxidation of ethanol is a major factor in causing hangovers. Increased serum acetate levels lead to accumulation of adenosine in many tissues including the brain, and administration of the adenosine receptor antagonist caffeine to rats after ethanol was found to decrease nociceptive behavior.


Acetic anhydride

Acetic anhydride, or ethanoic anhydride, is the chemical compound with the formula (CH3CO)2O. Commonly abbreviated Ac2O, it is the simplest isolatable acid anhydride and is a widely used reagent in organic synthesis. It is a colorless liquid that smells strongly of acetic acid, formed by its reaction with the moisture in the air.

Formic anhydride is an even simpler acid anhydride, but it spontaneously decomposes, especially once removed from solution.

Structure

Contrary to what its Lewis structure seems to predict, acetic anhydride, like many other acid anhydrides that are free to rotate, has experimentally been found to be aplanar. The pi system linkage through the central oxygen offers very weak resonance stabilization compared to the dipole-dipole repulsion between the two carbonyl oxygens. However, the energy barriers to bond rotation between each of the optimal aplanar conformations are quite low. .

Like most acid anhydrides, the carbonyl carbon of acetic anhydride is a potent electrophile as the leaving group for each carbonyl carbon (a carboxylate) is a good electron-withdrawing leaving group. The internal asymmetry may contribute to acetic anhydride's potent electrophilicity as the asymmetric geometry makes one side of a carbonyl carbon more reactive than the other, and in doing so tends to consolidate the electropositivity of a carbonyl carbon to one side (see electron density diagram).

Production

Acetic anhydride is produced by carbonylation of methyl acetate:

CH3CO2CH3 + CO → (CH3CO)2O

This process involves the conversion of methyl acetate to methyl iodide and an acetate salt. Carbonylation of the methyl iodide in turn affords acetyl iodide, which reacts with acetate salts or acetic acid to give the product. Rhodium iodide and lithium iodide are employed as catalysts. Because acetic anhydride is not stable in water, the conversion is conducted under anhydrous conditions. In contrast, the Monsanto acetic acid process, which also involves a rhodium catalyzed carbonylation of methyl iodide, is at least partially aqueous.

To a decreasing extent, acetic anhydride is also prepared by the reaction of ketene with acetic acid at 45–55 Â°C and low pressure (0.05–0.2 bar).

H2C=C=O + CH3COOH → (CH3CO)2O (ΔH = −63 kJ/mol)

Ketene is generated by dehydrating acetic acid at 700–750 Â°C in the presence of triethyl phosphate as a catalyst or (in Switzerland and the CIS) by the thermolysis of acetone at 600–700 Â°C in the presence of carbon disulfide as a catalyst.

CH3COOH H2C=C=O + H2O (ΔH = +147 kJ/mol)
CH3COCH3→ H2C=C=O + CH4

The route from acetic acid to acetic anhydride via ketene was developed by Wacker Chemie in 1922, when the demand for acetic anhydride increased due to the production of cellulose acetate.

Due to its low cost, acetic anhydride is purchased, not prepared, for use in research laboratories.

Reactions

Acetic anhydride is a versatile reagent for acetylations, the introduction of acetyl groups to organic substrates. In these conversions, acetic anhydride is viewed as a source of CH3CO+. Alcohols and amines are readily acetylated. For example, the reaction of acetic anhydride with ethanol yields ethyl acetate:

(CH3CO)2O + CH3CH2OH → CH3CO2CH2CH3 + CH3COOH

Often a base such as pyridine is added to function as catalyst. In specialized applications, Lewis acidic scandium salts have also proven effective catalysts.

Aromatic rings are acetylated, usually in the presence of an acid catalyst. Illustrative is the conversion of benzene to acetophenone:

(CH3CO)2O + C6H6→ CH3COC6H5 + CH3CO2H

Ferrocene may be acetylated too:

Cp2Fe + (CH3CO)2O → CpFe(C5H4COCH3)

Hydrolysis

Acetic anhydride dissolves in water to approximately 2.6% by weight. Aqueous solutions have limited stability because, like most acid anhydrides, acetic anhydride hydrolyses to give acetic acid:

(CH3CO)2O + H2O → 2 CH3CO2H

Applications

As indicated by its organic chemistry, Ac2O is mainly used for acetylations leading to commercially significant materials. Its largest application is for the conversion of cellulose to cellulose acetate, which is a component of ph

Acetal

An acetal is a molecule with two single bonded oxygens attached to the same carbon atom.

Traditional usages distinguish ketal from acetal (whereas a ketal has two carbon-bonded R groups and is formally derived from a ketone, an acetal has one or both carbon-bonded R groups as a hydrogen and is formally derived from an aldehyde). Current IUPAC terminology classifies ketals as a subset of acetals.

Formation of an acetal occurs when the hydroxyl group of a hemiacetal becomes protonated and is lost as water. The carbocation ion that is produced is then rapidly attacked by a molecule of alcohol. Loss of the proton from the attached alcohol gives the acetal.

Acetals are stable compared to hemiacetals but their formation is a reversible equilibrium as with esters. As a reaction to create an acetal proceeds, water must be removed from the reaction mixture, for example, with a Dean-Stark apparatus, lest it will hydrolyse the product back to the hemiacetal. The formation of acetals reduces the total number of molecules present and therefore is not favourable with regards to entropy. A way to improve this is to use an orthoester as a source of alcohol. Aldehydes and ketones undergo a process called acetal exchange with orthoesters to give acetals. Water produced along with the acetal product is used up in hydrolysing the orthoester and producing more alcohol to be used in the reaction.

Most glycosidic bonds in carbohydrates and other polysaccharides are acetal linkages. Acetaldehyde diethyl acetal is an important flavouring compound in distilled beverages.

The plastic known as acetal is a polyacetal of formaldehyde.

Acetals are used as protecting groups for carbonyl groups in organic synthesis as they are stable with respect to hydrolysis by bases and with respect to many oxidizing and reducing agents.

Examples


Ammonium acetate

Ammonium acetate is a chemical compound with the formula CH3COONH4 (or C2H4O2.NH3 or C2H7NO2). It is a white solid, which can be derived from the reaction of ammonia and acetic acid. It is available commercially and, depending on grade, can be rather inexpensive.

Uses and distinctive properties

As the salt of a weak acid and a weak base, ammoniumacetate has a number of distinctive properties.

  • NH4C2H3O2 is occasionally employed as a biodegradable de-icing agent.
  • It is often used with acetic acid to create a buffer solution, one that can be thermally decomposed to non-ionic products
  • Ammonium acetate is useful in the Knoevenagel condensation in organic synthesis.
  • It is relatively unusual example of a salt that melts at low temperatures.
  • Can be used with distilled water to make a protein precipitating reagent.
  • Is often used as an aqueous buffer for ESImass spectrometry of proteins and other molecules.

Ammonium acetate is volatile at low pressures. Because of this it has been used to replace cell buffers with non-volatile salts, in preparing samples for mass spectrometry. It is also popular as a buffer for mobile phases for HPLC with ELSD detection for this reason. Other volatile salts which have been used for this include ammonium formate.

Properties

CH3COONH4 is hygroscopic. It decomposes easily at elevated temperatures into acetamide.

CH3COONH4→ CH3C(O)NH2 + H2O

In this reaction, a salt is converted to two molecular species, which is a relatively uncommon conversion at mild temperatures.



From Yahoo Answers

Question:it has to be something that is household or easy for me to obtain

Answers:vinegar :)

Question:please help i dont understade ehat it means.....thanks

Answers:First of all, what is a buffer? A compounds that resists changes in pH when either acids or bases are added. A buffer is a mixture of a weak acid and its conjugate base. The workings of a buffer can be explained with Le Chatelier's principle. The acid is acetic acid and the conjugate base is the acetate ion, and the equilibrium is: HC2H3O2 <==> H+ + C2H3O2- As acid is added, the equilibrium shifts to the left to "use up" some of the added H+, while maintaining a relatively constant pH. If OH- is added, then it reacts with H+, reducing the hydrogen ion concentration and the equilibrium shifts right to make more H+, maintaining a relatively constant pH. The buffer capacity refers to how much acid and base the buffer can absorb. Clearly, you want the HC2H3O2 and C2H3O2- concentrations to be the same and as high as possible.

Question:

Answers:Potassium oxide. It is the only one containing 2 elements. CH3COOH - 3 elements HNO3 - 3 elements KOH - 3 elements K2O - 2 elements

Question:Acetic acid is found in vinegar. Explain why people can use white vinegar in preparing foods and in cooking without danger to the skin or internal organs.

Answers:Vinegar is a dilute solution of acetic acid (usually around 5% by weight). Acetic acid is a weak acid, meaning that it will only disassociate into H+ and acetate ions to a small degree when dissolved in water. This combination makes vinegar rather harmless compared to many other types of acidic solutions. Don t be fooled into thinking that all acids are these ultra-dangerous ( death in a bottle ) liquids. Many acids, some of which you might not even consider being an acid, are quite harmless and do not fit the common stereotype of what an acid is. For example, Vitamin C, otherwise known as Ascorbic acid, is an acid, but it is certainly not comparable to nitric acid in terms of how dangerous it is.

From Youtube

Acetic acid :3D model of acetic acid

Acetic Acid :Acetic acid is represented. A molecular model of acetic acid is shown using the Molecular Mania molecular modeling set from Zometool, Inc.