38:
175:
189:
354:
294:
Another way to avoid the entropic cost is to perform the synthesis by acetal exchange, using a pre-existing acetal-type reagent as the OR'-group donor rather than simple addition of alcohols themselves. One type of reagent used for this method is an orthoester. In this case, water produced along with
127:
was used specifically for the aldehyde-related cases (having at least one hydrogen in place of an R on the central carbon). The IUPAC originally deprecated the usage of the word ketal altogether, but has since reversed its decision. However, in contrast to historical usage, ketals are now a subset
365:
Formaldehyde forms a rich collection of acetals. This tendency reflects the fact that low molecular weight aldehydes are prone to self-condensation such that the C=O bond is replaced by an acetal. The acetal formed from
217:
the product back to the hemiacetal. The formation of acetals reduces the total number of molecules present (carbonyl + 2 alcohol → acetal + water) and therefore is generally not favourable with regards to
76:, while the R' groups must be organic fragments not hydrogen. The two R' groups can be equivalent to each other (a "symmetric acetal") or not (a "mixed acetal"). Acetals are formed from and convertible to
350:
auxiliaries. Indeed acetals of chiral glycols like, e.g. derivatives of tartaric acid can be asymmetrically opened with high selectivity. This enables the construction of new chiral centers.
421:(PSE) acetal is an example of arylsulfonyl acetal possessing atypical properties, like resistance to acid hydrolysis which leads to selective introduction and removal of the protective group.
131:
If one of the R groups has an oxygen as the first atom (that is, there are more than two oxygens single-bonded to the central carbon), the functional group is instead an
418:
693:
Chéry, Florence; Rollin, Patrick; De Lucchi, Ottorino; Cossu, Sergio (2000). "Phenylsulfonylethylidene (PSE) acetals as atypical carbohydrate-protective groups".
245:. They eliminate water. Since each step is often a rapid equilibrium, the reaction must be driven by removal of water. Methods for removing water include
347:
257:. Steps assumed to be involved: protonation of the carbonyl oxygen, addition of the alcohol to the protonated carbonyl, protonolysis of the resulting
641:
612:
805:
1724:
135:. In contrast to variations of R, both R' groups are organic fragments. If one R' is a hydrogen, the functional group is instead a
1729:
772:
739:
261:
or hemiketal, and addition of the second alcohol. These steps are illustrated with an aldehyde RCH=O and the alcohol R'OH:
101:
238:
that involve the formation of an acetal (or ketals) from aldehydes and ketones, respectively. These conversions are
209:. As a reaction to create an acetal proceeds, water must be removed from the reaction mixture, for example, with a
798:
312:
Since many sugars are polyhydroxy aldehydes and ketones, sugars are a rich source of acetals and ketals. Most
1628:
755:
Panten, Johannes; Surburg, Horst (2016). "Flavors and
Fragrances, 3. Aromatic and Heterocyclic Compounds".
398:(POM) plastic, also known as "acetal" or "polyacetal", is a polyacetal (and a polyether), and a polymer of
432:(acetaldehyde diethyl acetal), sometimes called simply "acetal", is an important flavouring compound in
1762:
1757:
1201:
791:
683:
Morrison, Robert T. and Boyd, Robert N., "Organic
Chemistry (6th ed)". p683. Prentice-Hall Inc (1992).
1238:
210:
1711:
246:
226:
molecule is used rather than two separate alcohol molecules (carbonyl + diol → acetal + water).
1611:
93:
1718:
1606:
1687:
1132:
295:
the acetal product is destroyed when it hydrolyses residual orthoester molecules, and this
202:
105:
8:
993:
163:
433:
429:
331:
89:
24:
706:
534:
also refers to any functional group that consists of a carbon bearing two heteroatoms
128:
of acetals, a term that now encompasses both aldehyde- and ketone-derived structures.
1677:
1647:
1405:
1027:
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735:
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46:
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54:
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321:
201:
Acetals are stable compared to hemiacetals but their formation is a reversible
1746:
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714:
650:, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "
621:, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "
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222:. One situation where it is not entropically unfavourable is when a single
37:
572:-acetal refers to compounds of type RRC(SR)(SR') (R,R' ≠ H, also known as
100:
compounds. The central carbon atom has four bonds to it, and is therefore
1682:
1635:
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436:. Two ketals of ethyl acetoacetate are used in commercial fragrances.
258:
151:
136:
132:
1558:
1472:
1437:
1422:
1410:
1253:
1228:
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383:
370:(two hydrogens attached to the central carbon) is sometimes called a
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1520:
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119:(both R groups organic fragments rather than hydrogen) rather than
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1303:
1298:
1263:
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219:
166:. Loss of the proton from the attached alcohol gives the acetal.
140:
1616:
1548:
1392:
1101:
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969:
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942:
888:
559:
353:
116:
81:
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31:
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206:
299:
also produces more alcohol to be used in the main reaction.
925:
239:
223:
162:
that is produced is then rapidly attacked by a molecule of
338:
as protecting groups used in research of modified sugars.
692:
115:
is sometimes used to identify structures associated with
139:, while if both are H, the functional group is a ketone
88:
at the central carbon, but have substantially different
514:), an propylene glycol ketal, a commercial fragrances.
72:
atom, with arbitrary other atoms attached to that) or
229:
68:. Here, the R groups can be organic fragments (a
1744:
360:
550:-acetal refers to compounds of type RRC(OR)(NR'
757:Ullmann's Encyclopedia of Industrial Chemistry
16:Organic compound with the structure >C(O–)2
799:
754:
475:), an ethylene glycol ketal, and fraistone (
328:is a ubiquitous example of a polyacetal.
806:
792:
731:Volatile Compounds in Foods and Beverages
424:
271:RCH=OH + R'OH ⇌ RCH(OH)(OR') + H
249:and trapping water with desiccants like
36:
522:Used in a more general sense, the term
276:RCH(OH)(OR') + H ⇌ RCH(OR') + H
234:Acetalisation and ketalization are the
146:Formation of an acetal occurs when the
1745:
727:
813:
787:
341:
517:
13:
647:Compendium of Chemical Terminology
618:Compendium of Chemical Terminology
413:
352:
14:
1774:
686:
346:Acetals also find application as
19:For the engineering plastic, see
285:RCH(OR') + R'OH ⇌ RCH(OR')
187:
173:
23:. For the flavor compound, see
748:
721:
677:
664:
635:
606:
378:group. The acetal formed from
230:Acetalisation and ketalization
1:
707:10.1016/s0040-4039(00)00199-4
600:
554:) (R,R' ≠ H) also known as a
361:Formaldehyde and acetaldehyde
180:Aldehyde to acetal conversion
96:as compared to the analogous
123:and, historically, the term
41:Generic structure of acetals
7:
728:Maarse, Henk (1991-03-29).
583:
302:
10:
1779:
194:Ketone to ketal conversion
158:and is lost as water. The
29:
18:
1701:
1660:
1580:
1557:
1519:
1496:
1391:
1312:
1182:
1159:
1115:
1058:
981:
956:
821:
307:
765:10.1002/14356007.t11_t02
419:Phenylsulfonylethylidene
266:RCH=O + H ⇌ RCH=OH
30:Not to be confused with
1712:chemical classification
660:10.1351/goldbook.G02661
631:10.1351/goldbook.K03376
382:is sometimes called an
247:azeotropic distillation
562:, a.k.a. aminoacetal.
425:Flavors and fragrances
386:. Formaldehyde forms
357:
57:with the connectivity
42:
1719:chemical nomenclature
356:
324:are acetal linkages.
143:or aldehyde hydrate.
40:
211:Dean–Stark apparatus
106:tetrahedral geometry
1175:not C, H or O)
695:Tetrahedron Letters
434:distilled beverages
1617:Hypervalent iodine
674:, S. 164–167.
430:1,1-Diethoxyethane
358:
342:Chiral derivatives
332:Benzylidene acetal
90:chemical stability
84:and have the same
43:
25:1,1-diethoxyethane
1763:Protecting groups
1758:Functional groups
1740:
1739:
1678:Sulfenyl chloride
1656:
1655:
1155:
1154:
974:(only C, H and O)
815:Functional groups
774:978-3-527-30673-2
759:. pp. 1–45.
741:978-0-8247-8390-7
701:(14): 2357–2360.
672:Protecting Groups
518:Related compounds
236:organic reactions
47:organic chemistry
1770:
1707:
1612:Trifluoromethoxy
1180:
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670:P.J. Kocieński:
668:
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610:
556:hemiaminal ether
542:. For example,
513:
474:
396:Polyoxymethylene
314:glycosidic bonds
290:
281:
272:
267:
255:molecular sieves
191:
177:
67:
55:functional group
21:Polyoxymethylene
1778:
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1607:Trichloromethyl
1602:Trifluoromethyl
1576:
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1356:Phosphine oxide
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414:Unusual acetals
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322:polysaccharides
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251:aluminium oxide
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1693:Sulfinylamines
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1670:
1668:Isothiocyanate
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1544:Selenenic acid
1541:
1539:Seleninic acid
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1534:Selenonic acid
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392:1,3,5-Trioxane
376:methylenedioxy
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1572:Telluroketone
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1458:Sulfonic acid
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1448:Sulfinic acid
1446:
1444:
1443:Thiosulfonate
1441:
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1436:
1434:
1433:Thiosulfinate
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1429:
1428:Sulfenic acid
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1383:Phosphaallene
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208:
204:
190:
176:
167:
165:
161:
157:
153:
149:
144:
142:
138:
134:
129:
126:
122:
118:
114:
109:
107:
103:
99:
95:
91:
87:
83:
79:
75:
71:
56:
52:
48:
39:
33:
26:
22:
1717:
1710:
1624:Vinyl halide
1581:
1511:Borinic acid
1506:Boronic acid
1483:Thioxanthate
988:
823:Hydrocarbons
756:
750:
730:
723:
698:
694:
688:
679:
671:
666:
645:
637:
616:
608:
595:Orthoformate
569:
565:
564:
555:
547:
543:
539:
535:
531:
527:
523:
521:
428:
417:
406:converts to
404:Acetaldehyde
400:formaldehyde
371:
368:formaldehyde
364:
345:
330:
311:
293:
233:
200:
145:
130:
124:
112:
110:
50:
44:
1688:Thiocyanate
1683:Sulfonamide
1648:Perchlorate
1636:Acyl halide
1597:Fluoroethyl
1478:Thionoester
1366:Phosphonium
1351:Phosphinate
1346:Phosphonous
1334:Phosphonate
1033:Hydroperoxy
855:Cyclopropyl
408:Metaldehyde
388:Paraldehyde
203:equilibrium
160:carbocation
150:group of a
1747:Categories
1592:Haloalkane
1463:Thioketone
1418:Persulfide
1314:Phosphorus
1279:Isocyanate
1269:Isonitrile
1170:or oxygen
1168:hydrogen,
1164:not being
1145:Orthoester
1038:Dioxiranes
1016:Enol ether
904:1-Propenyl
652:glycosides
601:References
590:Hemiaminal
578:thioketals
574:thioacetal
320:and other
259:hemiacetal
213:, lest it
156:protonated
152:hemiacetal
137:hemiacetal
133:orthoester
94:reactivity
1725:inorganic
1559:Tellurium
1473:Thioester
1438:Sulfoxide
1423:Disulfide
1411:Sulfonium
1361:Phosphine
1339:Phosphite
1322:Phosphate
1254:Carbamate
1229:Hydrazone
1162:element,
1160:Only one
1133:Anhydride
872:Methylene
715:0040-4039
384:acetonide
336:acetonide
326:Cellulose
243:catalysed
215:hydrolyse
121:aldehydes
111:The term
102:saturated
78:aldehydes
1706:See also
1641:Chloride
1567:Tellurol
1521:Selenium
1488:Xanthate
1202:Ammonium
1184:Nitrogen
1166:carbon,
1123:Carboxyl
1090:Aldehyde
1078:Acryloyl
1060:carbonyl
964:hydrogen
919:Cumulene
584:See also
438:Fructone
303:Examples
205:as with
154:becomes
148:hydroxyl
104:and has
98:carbonyl
74:hydrogen
1753:Acetals
1730:organic
1529:Selenol
1453:Sulfone
1406:Sulfide
1304:NONOate
1299:Nitroso
1289:Nitrite
1284:Nitrate
1274:Cyanate
1264:Nitrile
1249:Amidine
1244:Imidate
1214:Nitrene
1209:Hydrazo
1197:Enamine
1128:Acetoxy
1116:carboxy
1083:Benzoyl
1021:Epoxide
1004:Methoxy
994:Alcohol
948:Carbene
882:Methine
380:acetone
374:or the
220:entropy
164:alcohol
141:hydrate
117:ketones
82:ketones
1629:Iodide
1549:Selone
1393:Sulfur
1102:Ketone
1095:Ketene
1073:Acetyl
1028:Peroxy
999:Alkoxy
989:Acetal
970:oxygen
959:carbon
943:Alkyne
936:Benzyl
931:Phenyl
914:Allene
909:Crotyl
889:Alkene
877:Bridge
865:Pentyl
850:Propyl
840:Methyl
771:
738:
713:
623:ketals
560:Aminal
532:acetal
372:formal
348:chiral
308:Sugars
207:esters
125:acetal
70:carbon
63:C(OR')
51:acetal
32:acetyl
1661:Other
1498:Boron
1468:Thial
1401:Thiol
1294:Nitro
1259:Imide
1239:Amide
1224:Oxime
1219:Imine
1192:Amine
1140:Ester
1107:Ynone
1011:Ether
982:R-O-R
957:Only
899:Allyl
894:Vinyl
860:Butyl
845:Ethyl
835:Alkyl
642:IUPAC
613:IUPAC
113:ketal
53:is a
49:, an
1583:Halo
1068:Acyl
968:and
926:Aryl
769:ISBN
736:ISBN
711:ISSN
576:and
538:and
390:and
334:and
289:+ H
253:and
240:acid
224:diol
92:and
1234:Azo
761:doi
703:doi
656:doi
654:".
627:doi
625:".
558:or
497:)CH
481:C(O
458:)CH
446:C(O
316:in
80:or
45:In
1749::
966:,
961:,
767:.
709:.
699:41
697:.
644:,
615:,
580:.
501:CO
493:CH
477:CH
462:CO
442:CH
410:.
402:.
394:.
108:.
807:e
800:t
793:v
777:.
763::
744:.
717:.
705::
658::
629::
570:S
568:,
566:S
552:2
548:O
546:,
544:N
540:Y
536:X
530:-
528:Y
526:,
524:X
511:5
509:H
507:2
505:C
503:2
499:2
495:3
491:3
489:H
487:2
485:C
483:2
479:3
472:5
470:H
468:2
466:C
464:2
460:2
456:4
454:H
452:2
450:C
448:2
444:3
440:(
287:2
280:O
278:2
65:2
61:2
59:R
34:.
27:.
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