Phenolphthalein . It is an organic chemical compound of formula C 2 0H 14 O 4 . Widely used as a pH indicator to determine the acidity or basicity of solutions.
Summary
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- 1 Origin
- 2 Physical Properties
- 3 Obtaining
- 4 Applications
- 5 Precautions
- 6 Sources
Origin
The origin of the name of phenolphthalein, seems simple if we go back only to its chemical meaning, however from a remote point of view, phenol derives from the Greek phaino (nV4 <T), with the meaning of “I light up”, making it derive from benzol (C6H6), which had been discovered by Faraday as a residue of the gas from the London lighting , and phthalein, comes from the term naphtha, whose origin is very remote. It could be considered derived from the Egyptian Na-Ptah, because it was used in the worship of the Egyptian god of fire , Ptah (Ftha), equivalent to the Latin Vulcan, since it was a blackish liquid brought from Persia , which burned very well ( oil ). Naphthalene will be derived from itObtained in 1820, by Garden as residue from the distillation of the tar of coal , the naphthalene etc.
The first indicator to be synthesized was the phenolphthalein obtained by Baeyer by condensing the phthalic acid anhydride (orthobenzenedicarboxylic), with phenol, in 1871 . Many other indicators emerged from phenolphthalein, enhancing absorption changes by introducing sulfonated and brominated derivatives, studied by Lubs and Clark from 1915 . Thus appeared the phenol red , the thymol blue , the thymolphthalein , the bromothymol blue , bromophenol blue and cresol among others.
Earlier, in 1859 , the French Verguin had obtained fuchine 2, by chance oxidizing aniline with tin (IV) chloride , which was also obtained by Hofmann soon after. This compound would be the starting point for other indicators with triphenylmethane structure, such as methyl violet , methyl green , bright green, malachite green , etc., characterized by strong and bright shades at different pHs.
Another indicator synthesis route was azo dyes, which gave rise to methyl orange (proposed by Lunge in 1878 ). The second acid-base indicator of this type to be used was Congo red 3, discovered by Böttiger in 1884 . Then methyl red (introduced by Rupp and Loose in 1908 ), lizarin yellow etc. would be used.
Physical Properties
- Appearance: Solid
- Color: whiteor yellowish white
- Smell: Odorless
- colorless crystals
- soluble in waterand alcohol
- melting point of 254 ° C
- Composition: C 20H 14O 4 , C 2 H 5 OH
- Molecular weight: 318.33g / mol
- Melting point / freezingpoint 258 – 263 ° C
- Flammability ( solid, gas)
- Relative density: 1,299
- Internal Code: T1324, T1325, T1326
- CAS number: 77-09-8
- UN number: ND
- UN class: 3.2
Obtaining
It is obtained by reaction of phenol (C 6 H 5 OH) and phthalic anhydride (C 8 H 4 O 3 ), in the presence of sulfuric acid
Applications
- In chemistry it is used as a pH indicator, which in acidic solutions remains colorless, but in the presence of bases it turns red currant.
- Used in laboratory analysis in the 8.2 to 10 range, research, and fine chemistry.
- In chemical analysis it is used as an indicator of acid-base titrations, its turning point being around the pH value of 8.2 – 8.3, making the color transition from colorless to pink.
- Phenolphthalein is normally dissolved in alcoholfor use in experiments.
- As a diagnostic agent to investigate renal function and in the determination of residual urinein the bladder.
- In microbiology this chemical compound is used in the form of phenolphthalein diphosphate for the identification of specific bacteria(positive for acid phosphatase) in some selective culture media.
- It is used as a reagent in the Kastle-Meyer test, to detect traces of blood.
- In pharmacology and therapeutics it is used as acathartic laxative.
Cautions
- Store in tightly closed containers and dry environment. • In people with jaundice, phenolphthalein has no effect. Children under the age of two should not take it. Idiosyncrasy to the drug may occur.
