Results for acetal
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Dictionary:

acetal

  (ăs'ĭ-tăl') pronunciation
n.
  1. A colorless, flammable, volatile liquid, CH3CH(OC2H5)2, used in cosmetics and as a solvent.
  2. Any of the class of compounds formed from aldehydes combined with alcohol.

[ACET(O)– + AL(COHOL).]


 
 
Sci-Tech Encyclopedia: Acetal

A geminal diether (R1 = H). Ketals, considered a subclass of acetals, are also geminal diethers (R1 = C, aliphatic or aromatic). Acetals are (1) independent structural units or a part of certain biological and commercial polymers, (2) blocking or protecting groups for complex molecules undergoing selective synthetic transformations, and (3) entry compounds for independent organic chemical reactions. See also Polyacetal.

Acetals are easily prepared by the reaction of aldehydes with excess alcohol, under acid-catalyzed conditions. This is usually a two-step process (see reaction below) in which an aldehyde is


treated with an alcohol to yield a less stable hemiacetal, which then reacts with additional alcohol to give the acetal. Protonic or Lewis acids are effective catalysts for acetal formation; dehydrating agents, such as calcium chloride and molecular sieves, can also be used for molecules, such as sugars, where acids may cause problems. Less common acetal preparations are Grignard reagent condensation with orthoformates and mercuric-catalyzed additions of alcohols to acetylenes. See also Aldehyde; Ketone; Organic synthesis.

 
Veterinary Dictionary: acetal

An organic compound formed by a combination of an aldehyde with an alcohol.

 
Wikipedia: acetal
Structure of a generic acetal
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Structure of a generic acetal

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

Traditional usages distinguish ketal from acetals; where the acetal has one R group as H-. Current accepted terminology classifies ketals as a subset of acetals. For engineering applications, "acetal" is shorthand for the plastic polyoxymethylene, which is a polyacetal.

Formation of an acetal occurs when the hydroxyl group of a hemiacetal becomes protonated and is lost as water. The oxonium 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 reversible as with esters. As a reaction to create an acetal proceeds, water must be removed from the reaction mixture or it will hydrolyse the product. 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.

Acetals are important in nature, for example in solution the most stable form of glucose is its cyclic hemiacetal and maltose is an acetal made from two glucose units. Acetaldehyde diethyl acetal is an important flavouring compound in distilled beverages.[1]

Acetals are sometimes used as protecting groups for carbonyl groups in organic synthesis as they are stable with respect to hydrolysis by bases.

Acetal based plastics

Advantages of use of acetal based plastics

  • they are chemically resistant
  • they have a very low water absorption
  • resistant to hydrolysis by base

Disadvantages of use of acetal based plastics

  • low impact strength
  • low melting temperature
  • more rigid than nylons

References

  1. ^ Volatile Compounds in Foods and Beverages, ISBN 0824783905, http://books.google.com/books?id=_OvXjhLUz-oC, p.554

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

 
Translations: Translations for: Acetal

Dansk (Danish)
n. - acetal

Nederlands (Dutch)
acetaal (chemische verbinding)

Français (French)
n. - acétal

Deutsch (German)
n. - (chem.) Acetal

Ελληνική (Greek)
n. - (χημ.) ακετάλη

Italiano (Italian)
acetale

Português (Portuguese)
n. - acetal (m) (Quím.)

Русский (Russian)
ацеталь

Español (Spanish)
n. - acetal

Svenska (Swedish)
n. - acetal

中文（简体） (Chinese (Simplified))
乙缩醛, 乙缩醛二乙醇

中文（繁體） (Chinese (Traditional))
n. - 乙縮醛, 乙縮醛二乙醇

한국어 (Korean)
n. - 아세탈(수면제)

日本語 (Japanese)
n. - アセタール, アセタール樹脂

العربيه (Arabic)
‏(الاسم) أسيتال : سائل طيار عديم اللون‏

עברית (Hebrew)
n. - ‮תרכובת אורגנית שנוצרה מדחיסה של שתי פרודות אלכוהול עם פרודת אלדהיד, אצטאל (תרכובת)‬

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Copyrights:

Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2007. Published by Houghton Mifflin Company. All rights reserved.  Read more
Sci-Tech Encyclopedia. McGraw-Hill Encyclopedia of Science and Technology. Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved.  Read more
Veterinary Dictionary. Saunders Comprehensive Veterinary Dictionary 3rd Edition. Copyright © 2007 by D.C. Blood, V.P. Studdert and C.C. Gay, Elsevier. All rights reserved.  Read more
Wikipedia. This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Acetal".  Read more
Translations. Copyright © 2007, WizCom Technologies Ltd. All rights reserved.  Read more

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