メチルレッド

解説〘名〙 (methyl red) 赤～紫色の結晶。化学式は C15H15N3O2 酸塩基指示薬の一つ。酸性側で赤、塩基性側で黄色。変色域は pH4.4～6.2 塩素で酸化をうけ無色になるため、塩素検出にも用いられる。MR と略記される。精選版 日本国語大辞典 精選版

用途ｐH測定用、中和滴定用指示薬(弱塩基-強酸系)。

用途酸塩基中和滴定指示薬。

使用As indicator in 0.1% alcoholic solution; pH: 4.4 red, 6.2 yellow. Used for titrating NH3, weak organic bases, e.g., alkaloids; not suitable for organic acids, except oxalic and picric acid. Methyl red is easily reduced, thereby losing its color, and readings should be made promptly. It is gradually being replaced by sulfonphthalein indicators, such as bromcresol green, which are more stable and exhibit a sharper change in color.

一般的な説明Methyl red solution is an azo dye which turns to red when pH is below 4.4 (yellow pH < 6.2, orange pH 4.4-6.2). Some bacteria utilize glucose to form large amounts of acid with the result that the pH value of the medium falls distinct. Other species produce no or less free acid. This difference can be visualized by using methyl red. This test is used to differentiate enteric bacteria.

製造方法2-Aminobenzoic aciddiazo, and N,N-dimethylaniline coupling.

純化方法The acid is extracted with boiling toluene using a Soxhlet apparatus. The crystals which separate on slow cooling to room temperature are filtered off, washed with a little toluene and recrystallised from glacial acetic acid, *benzene or toluene followed by pyridine/water. Alternatively, dissolve it in aqueous 5% NaHCO3 solution, and precipitate it from a hot solution by dropwise addition of aqueous HCl. Repeat this until the extinction coefficients do not increase. [Beilstein 16 IV 504.]

定義An acid–base indicator that is red in solutions below a pH of 4.2 and yellow above a pH of 6.3. It is often used for the same types of titration as methyl orange but the transition range of methyl red is nearer neutral (pH7) than that of methyl orange. The two molecules are structurally similar.