Hydrolysis 14385 223346530 2008-07-03T17:58:31Z AlexandriNo 1640494 '''Hydrolysis''' is a [[chemical reaction]] or process in which a [[chemical compound]] is broken down by reaction with [[water (molecule)|water]].<ref>[[Compendium of Chemical Terminology]], [http://goldbook.iupac.org/H02902.html hydrolysis], accessed [[2007-01-23]].</ref><ref>[[Compendium of Chemical Terminology]], [http://goldbook.iupac.org/S05762.html solvolysis], accessed [[2007-01-23]].</ref> It is the type of reaction that is used to break down certain [[polymer]]s, especially those made by [[step-growth polymerization]]. Such [[polymer degradation]] is usually catalysed by either [[acid]] or [[alkali]] attack, often increasing with their strength or [[pH]]. ==Types== In [[organic chemistry]], hydrolysis can be considered as the reverse or opposite of [[condensation reaction|condensation]], a reaction in which two molecular fragments are joined for each water molecule produced. As hydrolysis may be a reversible reaction, condensation and hydrolysis can take place at the same time, with the position of equilibrium determining the amount of each product. In [[inorganic chemistry]], the word is often applied to solutions of salts and the reactions by which they are converted to new ionic species or to precipitates (oxides, hydroxides, or salts). The addition of a molecule of water to a chemical compound, without forming any other products is usually known as [[hydration reaction|hydration]], rather than ''hydrolysis''. In [[biochemistry]], hydrolysis is considered the reverse or opposite of [[dehydration synthesis]]. In hydrolysis, a water molecule (H<sub>2</sub>O), is added, whereas in dehydration synthesis, a molecule of water is removed. In [[electrochemistry]], hydrolysis can also refer to the [[electrolysis of water]]. In hydrolysis, a voltage is applied across an aqueous medium, which produces a current and breaks the water into its constituents, hydrogen and oxygen. In [[polymer chemistry]], hydrolysis of [[polymer]]s can occur during high-temperature processing such as [[injection moulding]] leading to chain degradation and loss of product integrity. Polymers most at risk include [[PET]], [[polycarbonate]], [[nylon]] and other polymers made by [[step-growth polymerization]]. Such materials must be dried prior to moulding. == Hydrolysis of amide links == In other hydrolysis reactions, such as hydrolysis of an [[amide]] link into a [[carboxylic acid]] and an [[amine]] product or [[ammonia]], only the carboxylic acid product has a hydroxyl group derived from the water. The amine product (or ammonia) gains the remaining hydrogen ion. A more specific case of the hydrolysis of an amide link is hydrolyzing the [[peptide link]]s of [[amino acid]]s. Many [[polyamide]] polymers such as [[nylon 6,6]] are attacked and hydrolysed by strong acids. Such attack leads to [[depolymerization]] and nylon products fail by fracturing when exposed to even small amounts of acid. The reaction is essentially the reverse of the synthesis from monomers: [[Image:Condensation polymerization diacid diamine.svg|400px]]{{clear}} Other polymers made by [[step-growth polymerization]] are susceptible to similar [[polymer degradation]] reactions. The problem is known as [[stress corrosion cracking]]. == Hydrolysis of metal salts == (As noted above, hydrolysis of metal salts is more commonly known as hydration.) Many metal ions are strong [[Lewis acid]]s, and in water they may undergo hydrolysis to form ''basic salts''. Such salts contain a [[hydroxyl]] group that is directly bound to the metal ion in place of a water [[ligand]]. The positive charge on metal ions creates an attraction to water, a [[Lewis base]] with a non-binding electron pair on the [[oxygen]] atom, and alters water's electron density. This in turn increases the [[Chemical polarity| polarity]] of the O-H bond, which now acts as a proton donor under [[Brønsted-Lowry acid-base theory]] to release the hydrogen as a H+ ion, increasing the acidity of the solution. For example, [[aluminium chloride]] undergoes extensive hydrolysis in water such that the solution becomes very acidic. :<math>[Al(H_2 O)_6]^{3+} \underset{\ H_3 O^+}{\overset{H_2 O}{\rightleftharpoons}} [Al(OH)(H_2 O)_5]^{2+}</math> This implies that [[hydrogen chloride]] is lost in the evaporation of AlCl<sub>3</sub> solutions and the residue is a basic salt (in this case an ''oxychloride'') in place of AlCl<sub>3</sub>. Such behaviour is also seen with other metal chlorides such as [[zinc chloride|ZnCl<sub>2</sub>]], [[Tin(II) chloride|SnCl<sub>2</sub>]], [[Iron(III) chloride|FeCl<sub>3</sub>]] and lanthanide halides such as [[Dysprosium(III) chloride|DyCl<sub>3</sub>]]. With some compounds such as [[titanium tetrachloride|TiCl<sub>4</sub>]], the hydrolysis may go to completion and form the pure [[hydroxide]] or [[oxide]], in this case [[Titanium dioxide|TiO<sub>2</sub>]]. == Hydrolysis of cellulose (Cellulolysis) == {{Main|Cellulase}} Cellulolytic is relating to or causing the hydrolysis of [[cellulose]] (i.e. cellulolytic [[bacteria]], [[fungi]] or [[enzyme]]s). The hydrolysis into glucose (i.e. of cellulose or starch) is called '''saccharification'''. == Irreversibility of hydrolysis under physiological conditions == Under physiological conditions (i.e. in dilute aqueous solution), a hydrolytic cleavage reaction, where the concentration of a metabolic precursor is low (on the order of 10<sup>-3</sup> to 10<sup>-6</sup> molar), is essentially [[thermodynamics|thermodynamically]] irreversible. To give an example: : A + H<sub>2</sub>O → X + Y : <math>K_d = \frac{\left[X\right] \left[Y\right]} {\left[H_2O\right] \left[A\right]}</math> Assuming that ''x'' is the final concentration of products, and that ''C'' is the initial concentration of A, and W = [H<sub>2</sub>O] = 55.5 molar, then ''x'' can be calculated with the equation: : <math>\frac{x \times x}{W\left(C - x\right)} = K_d</math> let K<sub>d</sub>×W = k: then <math> x = \frac {-k + \sqrt {k^2 + 4kC} } {2}. </math> For a value of C = 0.001 molar, and k = 1 molar, ''x''/C &gt; 0.999. Less than 0.1% of the original reactant would be present once the reaction is complete. This theme of physiological irreversibility of hydrolysis is used consistently in metabolic pathways, since many biological processes are driven by the cleavage of [[anhydride|anhydrous]] [[pyrophosphate]] bonds. == See also == * [[Adenosine triphosphate]] * [[Dehydration synthesis]] * [[Polymer degradation]] * [[Solvolysis]] == References == <references/> ==External links== {{commons|Collagen|Collagen}} * [http://macromoleculeinsights.com/collagen.php Molecular Structure] * [http://www.hydrolyzed-collagen.com Hydrolyzed Collagen (Gelatin)] [[Category:Chemical reactions]] [[bs:Hidroliza]] [[bg:Хидролиза]] [[ca:Hidròlisi]] [[cs:Hydrolýza]] [[da:Hydrolyse]] [[de:Hydrolyse]] [[es:Hidrólisis]] [[eo:Hidrolizo]] [[fr:Hydrolyse]] [[ko:가수분해]] [[it:Idrolisi]] [[he:הידרוליזה]] [[lv:Hidrolīze]] [[lt:Hidrolizė]] [[mk:Хидролиза]] [[nl:Hydrolyse]] [[ja:加水分解]] [[no:Hydrolyse]] [[pl:Hydroliza]] [[pt:Hidrólise]] [[ro:Reacţia de hidroliză]] [[ru:Гидролиз]] [[sq:Hidrolizë]] [[simple:Hydrolysis]] [[sk:Hydrolýza]] [[sr:Хидролиза]] [[sh:Hidroliza]] [[su:Hidrolisis]] [[fi:Hydrolyysi]] [[sv:Hydrolys]] [[tr:Hidroliz]] [[uk:Гідроліз]] [[zh:水解]]