Hydrolysis

Japanese: 加水分解 - かすいぶんかい(英語表記)hydrolysis
Hydrolysis

The decomposition reaction that occurs when a solute in an aqueous solution reacts with water molecules is called hydrolysis. The decomposition reaction that occurs between a solute and a solvent molecule in any solution, not limited to water, is called solvolysis.

In an aqueous solution of a weak acid HA and a salt of a strong base MOH, MA, the A- ions (negative ions) react with some of the water molecules to produce hydroxide ions (equation 1). In the case of an aqueous solution of a strong acid HX and a salt of a weak base BOH, BX, the B + ions (positive ions) react to produce hydrogen ions (equation 2).


These equilibria are called hydrolysis equilibria, and solutions of MA salts are basic, while solutions of BX salts are acidic. When strong acid salts of polyvalent metal ions such as Al 3+ and Fe 3+ are dissolved in water, these metal ions undergo hydrolysis.


As the hydrolysis progresses, the hydroxide is produced, and the solution may form a colloid or precipitate.


Organic compounds such as fats, esters, acid amides, proteins, peptides, and sugars can also undergo hydrolysis, but this generally takes the form of a metathesis reaction in which a water molecule splits into H and OH. Take the hydrolysis of an ester as an example:

However, the reaction rate is relatively slow, and acids or bases are often used as catalysts. In organic synthesis and industrial chemistry, as well as in biochemistry, important reactions catalyzed by hydrolases are known.

[Iwamoto Shinbu]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

水溶液中の溶質が水分子と反応しておこす分解反応をいい水解ともいう。水に限らず、溶液中で溶質と溶媒分子とでおこる分解反応は加溶媒分解ソルボリシスsolvolysisという。

 弱酸HAと強塩基MOHの塩MAの水溶液ではA-イオン(陰イオン)が、一部水分子と反応して水酸化物イオンを生じ(式1)、また強酸HXと弱塩基BOHの塩BXの場合は、B+イオン(陽イオン)が反応して水素イオンを生ずる(式2)。


これらの平衡を加水分解平衡といい、MA塩の溶液は塩基性、BX塩の溶液は酸性を呈する。Al3+、Fe3+などの多価金属イオンの強酸塩を水に溶かすと、これらの金属イオンは加水分解を受ける。


加水分解が進行すると水酸化物になり、コロイド化したり、沈殿になったりする。


 脂肪、エステル、酸アミド、タンパク質、ペプチド、糖などの有機化合物も加水分解を受けるが、一般に水分子がHとOHに分かれる複分解反応の形式をとる。エステルの加水分解を例にとると、

となるが、反応速度は比較的遅く、酸や塩基が触媒となることが多い。有機合成や工業化学におけるとともに、生化学においても加水分解酵素が触媒となる重要な反応が知られている。

[岩本振武]

出典 小学館 日本大百科全書(ニッポニカ)日本大百科全書(ニッポニカ)について 情報 | 凡例

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