Hydrolysis

Generic hydrolysis reaction. (The 2-way yield symbol indicates achemical equilibriumin which hydrolysis andcondensationare reversible.)

Hydrolysis(/haɪˈdrɒlɪsɪs/;fromAncient Greekhydro-'water' andlysis'to unbind') is any chemical reaction in which a molecule ofwaterbreaks one or more chemical bonds. The term is used broadly forsubstitution,elimination,andsolvationreactions in which water is thenucleophile.^[1]

Biological hydrolysis is the cleavage ofbiomoleculeswhere a water molecule is consumed to effect the separation of a larger molecule into component parts. When acarbohydrateis broken into its component sugar molecules by hydrolysis (e.g.,sucrosebeing broken down intoglucoseandfructose), this is recognized assaccharification.^[2]

Hydrolysis reactions can be the reverse of acondensation reactionin which two molecules join into a larger one and eject a water molecule. Thus hydrolysis adds water to break down, whereas condensation builds up by removing water.^[3]

Types

Usually hydrolysis is a chemical process in which a molecule of water is added to a substance. Sometimes this addition causes both the substance and water molecule to split into two parts. In such reactions, one fragment of the target molecule (or parent molecule) gains ahydrogen ion.It breaks a chemical bond in the compound.

Salts

A common kind of hydrolysis occurs when asaltof aweak acidorweak base(or both) is dissolved in water.Water spontaneously ionizesintohydroxide anionsandhydronium cations.The salt also dissociates into its constituent anions and cations. For example,sodium acetatedissociates in water intosodiumandacetateions. Sodium ions react very little with the hydroxide ions whereas the acetate ions combine with hydronium ions to produceacetic acid.In this case the net result is a relative excess of hydroxide ions, yielding a basicsolution.

Strong acidsalso undergo hydrolysis. For example, dissolvingsulfuric acid(H₂SO₄) in water is accompanied by hydrolysis to givehydroniumandbisulfate,the sulfuric acid'sconjugate base.For a more technical discussion of what occurs during such a hydrolysis, seeBrønsted–Lowry acid–base theory.

Esters and amides

Acid–base-catalysed hydrolyses are very common; one example is the hydrolysis ofamidesoresters.Their hydrolysis occurs when thenucleophile(a nucleus-seeking agent, e.g., water or hydroxyl ion) attacks the carbon of thecarbonyl groupof theesteroramide.In an aqueous base, hydroxyl ions are better nucleophiles than polar molecules such as water. In acids, the carbonyl group becomes protonated, and this leads to a much easier nucleophilic attack. The products for both hydrolyses are compounds withcarboxylic acidgroups.

Perhaps the oldest commercially practiced example of ester hydrolysis issaponification(formation of soap). It is the hydrolysis of atriglyceride(fat) with an aqueous base such assodium hydroxide(NaOH). During the process,glycerolis formed, and thefatty acidsreact with the base, converting them to salts. These salts are called soaps, commonly used in households.

In addition, in living systems, most biochemical reactions (including ATP hydrolysis) take place during the catalysis ofenzymes.The catalytic action of enzymes allows the hydrolysis ofproteins,fats, oils, andcarbohydrates.As an example, one may considerproteases(enzymes that aiddigestionby causing hydrolysis ofpeptide bondsinproteins). They catalyze the hydrolysis of interior peptide bonds in peptide chains, as opposed toexopeptidases(another class of enzymes, that catalyze the hydrolysis of terminal peptide bonds, liberating one free amino acid at a time).

However, proteases do not catalyze the hydrolysis of all kinds of proteins. Their action is stereo-selective: Only proteins with a certain tertiary structure are targeted as some kind of orienting force is needed to place the amide group in the proper position for catalysis. The necessary contacts between an enzyme and its substrates (proteins) are created because the enzyme folds in such a way as to form a crevice into which the substrate fits; the crevice also contains the catalytic groups. Therefore, proteins that do not fit into the crevice will not undergo hydrolysis. This specificity preserves the integrity of other proteins such ashormones,and therefore the biological system continues to function normally.

Mechanism for acid-catalyzed hydrolysis of an amide.

Upon hydrolysis, anamideconverts into acarboxylic acidand anamineorammonia(which in the presence of acid are immediately converted to ammonium salts). One of the two oxygen groups on the carboxylic acid are derived from a water molecule and the amine (or ammonia) gains the hydrogen ion. The hydrolysis ofpeptidesgivesamino acids.

Manypolyamidepolymers such asnylon 6,6hydrolyze in the presence of strong acids. The process leads todepolymerization.For this reason nylon products fail by fracturing when exposed to small amounts of acidic water. Polyesters are also susceptible to similarpolymer degradationreactions. The problem is known asenvironmental stress cracking.

ATP

Hydrolysis is related toenergy metabolismand storage. All living cells require a continual supply of energy for two main purposes: thebiosynthesisof micro and macromolecules, and the active transport of ions and molecules across cell membranes. The energy derived from theoxidationof nutrients is not used directly but, by means of a complex and long sequence of reactions, it is channeled into a special energy-storage molecule,adenosine triphosphate(ATP). The ATP molecule containspyrophosphatelinkages (bonds formed when two phosphate units are combined) that release energy when needed. ATP can undergo hydrolysis in two ways: Firstly, the removal of terminal phosphate to formadenosine diphosphate(ADP) and inorganic phosphate, with the reaction:

{\ce {ATP + H2O -> ADP + P_{i}}}

Secondly, the removal of a terminal diphosphate to yieldadenosine monophosphate(AMP) andpyrophosphate.The latter usually undergoes further cleavage into its two constituent phosphates. This results in biosynthesis reactions, which usually occur in chains, that can be driven in the direction of synthesis when the phosphate bonds have undergone hydrolysis.

Polysaccharides

Sucrose. The glycoside bond is represented by the central oxygen atom, which holds the two monosaccharide units together.

Monosaccharidescan be linked together byglycosidic bonds,which can be cleaved by hydrolysis. Two, three, several or many monosaccharides thus linked formdisaccharides,trisaccharides,oligosaccharides,orpolysaccharides,respectively. Enzymes that hydrolyze glycosidic bonds are called "glycoside hydrolases"or" glycosidases ".

The best-known disaccharide issucrose(table sugar). Hydrolysis of sucrose yieldsglucoseandfructose.Invertaseis asucraseused industrially for the hydrolysis of sucrose to so-calledinvert sugar.Lactaseis essential for digestive hydrolysis oflactosein milk; many adult humans do not produce lactase andcannot digest the lactosein milk.

The hydrolysis of polysaccharides to soluble sugars can be recognized assaccharification.^[2]Malt made frombarleyis used as a source of β-amylase to break downstarchinto the disaccharidemaltose,which can be used by yeast toproduce beer.Otheramylaseenzymes may convert starch to glucose or to oligosaccharides.Celluloseis first hydrolyzed tocellobiosebycellulaseand then cellobiose is further hydrolyzed toglucosebybeta-glucosidase.Ruminantssuch as cows are able to hydrolyze cellulose into cellobiose and then glucose because ofsymbioticbacteria that produce cellulases.

DNA

Hydrolysis ofDNAoccurs at a significant rate in vivo.^[4]For example, it is estimated that in each human cell 2,000 to 10,000 DNApurinebases turn over every day due to hydrolytic depurination, and that this is largely counteracted by specific rapidDNA repairprocesses.^[4]Hydrolytic DNA damages that fail to be accurately repaired may contribute tocarcinogenesisandageing.^[4]

Metal aqua ions

Metal ions areLewis acids,and inaqueous solutionthey formmetal aquo complexesof the general formulaM(H₂O)_n^m+.^[5]^[6]The aqua ions undergo hydrolysis, to a greater or lesser extent. The first hydrolysis step is given generically as

{\ce {M(H2O)_{\mathit {n}}^{{\mathit {m}}+}{}+H2O<=>M(H2O)_{{\mathit {n}}-1}(OH)^{({\mathit {m}}-1){}+}{}+H3O+}}

Thus the aquacationsbehave as acids in terms ofBrønsted–Lowry acid–base theory.This effect is easily explained by considering theinductive effectof the positively charged metal ion, which weakens theO−Hbond of an attached water molecule, making the liberation of a proton relatively easy.

Thedissociation constant,pK_a,for this reaction is more or less linearly related to the charge-to-size ratio of the metal ion.^[7]Ions with low charges, such asNa⁺are very weak acids with almost imperceptible hydrolysis. Large divalent ions such asCa²⁺,Zn²⁺,Sn²⁺andPb²⁺have a pK_aof 6 or more and would not normally be classed as acids, but small divalent ions such asBe²⁺undergo extensive hydrolysis. Trivalent ions likeAl³⁺andFe³⁺are weak acids whose pK_ais comparable to that ofacetic acid.Solutions of salts such asBeCl₂orAl(NO₃)₃in water are noticeablyacidic;the hydrolysis can besuppressedby adding an acid such asnitric acid,making the solution more acidic.

Hydrolysis may proceed beyond the first step, often with the formation of polynuclear species via the process ofolation.^[7]Some "exotic" species such asSn₃(OH)2+4^[8]are well characterized. Hydrolysis tends to proceed aspHrises leading, in many cases, to the precipitation of a hydroxide such asAl(OH)₃orAlO(OH).These substances, major constituents ofbauxite,are known aslateritesand are formed by leaching from rocks of most of the ions other than aluminium and iron and subsequent hydrolysis of the remaining aluminium and iron.

Mechanism strategies

Acetals,imines,andenaminescan be converted back intoketonesby treatment with excess water under acid-catalyzed conditions:RO·OR−H₃O−O;NR·H₃O−O;RNR−H₃O−O.^[9]

Catalysis

Acidic hydrolysis

Acid catalysiscan be applied to hydrolyses.^[10]For example, in the conversion ofcelluloseorstarchtoglucose.^[11]^[12]^[13]Carboxylic acids can be produced from acid hydrolysis of esters.^[14]

Acids catalyze hydrolysis ofnitrilesto amides. Acid hydrolysisdoes notusually refer to the acid catalyzed addition of the elements of water to double or triple bonds byelectrophilic additionas may originate from ahydration reaction.Acid hydrolysis is used to prepare monosaccharide with the help ofmineral acidsbut formic acid andtrifluoroacetic acidhave been used.^[15]

Acid hydrolysis can be utilized in the pretreatment of cellulosic material, so as to cut the interchain linkages in hemicellulose and cellulose.^[16]

Alkaline hydrolysis

Alkaline hydrolysis usually refers to types ofnucleophilic substitutionreactions in which the attackingnucleophileis ahydroxide ion.The best known type issaponification:cleavingestersintocarboxylatesalts andalcohols.Inester hydrolysis,the hydroxide ion nucleophile attacks thecarbonylcarbon. This mechanism is supported byisotope labelingexperiments. For example, whenethyl propionatewith anoxygen-18labeled ethoxy group is treated withsodium hydroxide(NaOH), the oxygen-18 is completely absent from thesodium propionateproduct and is found exclusively in theethanolformed.^[17]

The reaction is often used to solubilize solid organic matter.Chemical drain cleanerstake advantage of this method to dissolve hair and fat in pipes. The reaction is also used todispose of human and other animal remainsas an alternative to traditional burial or cremation.

References

^IUPAC,Compendium of Chemical Terminology,2nd ed. (the "Gold Book" ) (1997). Online corrected version: (2006–) "Hydrolysis".doi:10.1351/goldbook.H02902 IUPAC,Compendium of Chemical Terminology,2nd ed. (the "Gold Book" ) (1997). Online corrected version: (2006–) "Solvolysis".doi:10.1351/goldbook.S05762
^^a ^b"Definition of Saccharification".Merriam-Webster.Archivedfrom the original on 7 January 2021.Retrieved8 September2020.
^Steane, Richard."Condensation and Hydrolysis".www.biotopics.co.uk.Archivedfrom the original on 2020-11-27.Retrieved2020-11-13.
^^a ^b ^cLindahl T. Instability and decay of the primary structure of DNA. Nature. 1993 Apr 22;362(6422):709-15. doi: 10.1038/362709a0. PMID 8469282
^Burgess, John (1978).Metal Ions in Solution.Chichester: Ellis Horwood.ISBN 978-0853120278.
^Richens, D. T. (1997).The Chemistry of Aqua Ions: Synthesis, Structure, and Reactivity: A Tour through the Periodic Table of the Elements.Wiley.ISBN 0-471-97058-1.
^^a ^bBaes, Charles F.; Mesmer, Robert E. (1976).The Hydrolysis of Cations.New York: Wiley.ISBN 9780471039853.
^Greenwood, Norman N.;Earnshaw, Alan (1997).Chemistry of the Elements(2nd ed.).Butterworth-Heinemann.p. 384.ISBN 978-0-08-037941-8.
^Klein, David (2012).Organic Chemistry.Wiley.ISBN 978-0-471-75614-9.
^Speight, James G. (2 November 2016).Hydrolysis.pp. 143–144.ISBN 9780128006689.inSpeight, James G. (2017). "Industrial Organic Chemistry".Environmental Organic Chemistry for Engineers.pp. 87–151.doi:10.1016/B978-0-12-804492-6.00003-4.ISBN 978-0-12-804492-6.
^Goldstein, Irving S. (1983). "Hydrolysis of Cellulose by Acids".Biomass Utilization.pp. 559–566.doi:10.1007/978-1-4757-0833-2_30.ISBN 978-1-4757-0835-6.
^US 5726046,Farone, William A. & Cuzens, John E., "Method of producing sugars using strong acid hydrolysis", published 1998-03-10, assigned to Arkenol Inc.
^Vaughn, H. L.; Robbins, M. D. (April 1975). "Rapid procedure for the hydrolysis of amides to acids".The Journal of Organic Chemistry.40(8): 1187–1189.doi:10.1021/jo00896a050.
^"5.4: Hydrolysis Reactions".Chemistry LibreTexts.2021-08-04.Retrieved2023-10-07.
^Chen, Hongzheng (2015).Lignocellulose Biorefinery Engineering.Woodhead Publishing.ISBN 978-0-08-100135-6.
^Pandey; Larroche; Ricke; Dussap; Gnansounou (2011).Biofuels: Alternaative Feedstocks and Conversion Processes.Academic press.ISBN 978-0-12-385099-7.
^McMurry, John (1996).Organic Chemistry(4th ed.). Pacific Grove, CA: Brooks/Cole Publishing Company. pp.820–821.ISBN 0534238327.

[1] IUPAC,Compendium of Chemical Terminology,2nd ed. (the "Gold Book" ) (1997). Online corrected version: (2006–) "Hydrolysis".doi:10.1351/goldbook.H02902 IUPAC,Compendium of Chemical Terminology,2nd ed. (the "Gold Book" ) (1997). Online corrected version: (2006–) "Solvolysis".doi:10.1351/goldbook.S05762

[saccharification-2] "Definition of Saccharification".Merriam-Webster.Archivedfrom the original on 7 January 2021.Retrieved8 September2020.

[3] Steane, Richard."Condensation and Hydrolysis".www.biotopics.co.uk.Archivedfrom the original on 2020-11-27.Retrieved2020-11-13.

[Lindahl1993-4] Lindahl T. Instability and decay of the primary structure of DNA. Nature. 1993 Apr 22;362(6422):709-15. doi: 10.1038/362709a0. PMID 8469282

[5] Burgess, John (1978).Metal Ions in Solution.Chichester: Ellis Horwood.ISBN 978-0853120278.

[6] Richens, D. T. (1997).The Chemistry of Aqua Ions: Synthesis, Structure, and Reactivity: A Tour through the Periodic Table of the Elements.Wiley.ISBN 0-471-97058-1.

[bm-7] Baes, Charles F.; Mesmer, Robert E. (1976).The Hydrolysis of Cations.New York: Wiley.ISBN 9780471039853.

[8] Greenwood, Norman N.;Earnshaw, Alan (1997).Chemistry of the Elements(2nd ed.).Butterworth-Heinemann.p. 384.ISBN 978-0-08-037941-8.

[9] Klein, David (2012).Organic Chemistry.Wiley.ISBN 978-0-471-75614-9.

[10] Speight, James G. (2 November 2016).Hydrolysis.pp. 143–144.ISBN 9780128006689.inSpeight, James G. (2017). "Industrial Organic Chemistry".Environmental Organic Chemistry for Engineers.pp. 87–151.doi:10.1016/B978-0-12-804492-6.00003-4.ISBN 978-0-12-804492-6.

[11] Goldstein, Irving S. (1983). "Hydrolysis of Cellulose by Acids".Biomass Utilization.pp. 559–566.doi:10.1007/978-1-4757-0833-2_30.ISBN 978-1-4757-0835-6.

[12] US 5726046,Farone, William A. & Cuzens, John E., "Method of producing sugars using strong acid hydrolysis", published 1998-03-10, assigned to Arkenol Inc.

[13] Vaughn, H. L.; Robbins, M. D. (April 1975). "Rapid procedure for the hydrolysis of amides to acids".The Journal of Organic Chemistry.40(8): 1187–1189.doi:10.1021/jo00896a050.

[14] "5.4: Hydrolysis Reactions".Chemistry LibreTexts.2021-08-04.Retrieved2023-10-07.

[15] Chen, Hongzheng (2015).Lignocellulose Biorefinery Engineering.Woodhead Publishing.ISBN 978-0-08-100135-6.

[16] Pandey; Larroche; Ricke; Dussap; Gnansounou (2011).Biofuels: Alternaative Feedstocks and Conversion Processes.Academic press.ISBN 978-0-12-385099-7.

[mcmurry-17] McMurry, John (1996).Organic Chemistry(4th ed.). Pacific Grove, CA: Brooks/Cole Publishing Company. pp.820–821.ISBN 0534238327.

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