PHENOLPHTHALEIN

Phenolphthalein is the most important inorganic oxygen acid of phosphorus.
Phenolphthalein is diluted from 93% concentration down to the preferred percentage. 
Phenolphthalein is available in different grades and for a variety of applications. Various applications require specific grades. 

CAS Number: 77-09-8
Molecular Formula: C20H14O4
Molecular Weight: 318.32
EINECS Number: 201-004-7

Synonyms: phenolphthalein, 77-09-8, Phthalimetten, Euchessina, Phenolax, Phthalin, Espotabs, Purgophen, Koprol, Laxogen, Trilax, Purga, Spulmako-lax, Chocolax, Purgen, Dihydroxyphthalophenone, Phenolphtaleine, Correctol, Medilax, Colax, Laxin, 3,3-Bis(4-hydroxyphenyl)phthalide, FemiLax, Ex-Lax, 3,3-Bis(4-hydroxyphenyl)-1(3H)-isobenzofuranone, Fenolftalein, Fenolftaleina, 1(3H)-Isobenzofuranone, 3,3-bis(4-hydroxyphenyl)-, 3,3-Bis(p-hydroxyphenyl)phthalide, 3,3-bis(4-hydroxyphenyl)-2-benzofuran-1-one, NCI-C55798, Phenolphthaleinum, alpha-Di(p-hydroxyphenyl)phthalide, 3,3-bis(4-hydroxyphenyl)-1,3-dihydro-2-benzofuran-1-one, DTXSID0021125, 6QK969R2IF, NSC-10464, DTXCID901125, CHEBI:34914, NSC10464, Laxettes, RefChem:6481, A06AB04, 201-004-7, o-Toluic acid, alpha-(p-hydroxyphenyl)-alpha-4-oxo-2,5-cyclohexadien-1-ylidene-, Prulet, 3,3-Bis(4-hydroxyphenyl)isobenzofuran-1(3H)-one, Alophen, Phillips Gelcaps, Phenophthalein, MFCD00005913, Feen-A-Mint Laxative Mints, 3,3-Bis(4-hydroxyphenyl)-2-benzofuran-1(3H)-one, NSC 10464, component of Agoral, Phenolphthalein, white, Phthalide 3,3,-bis(p-hydroxyphenyl)-, Phenolphthalein solution, CHEMBL63857, MLS000069592, 3,3-bis(4-hydroxyphenyl)isobenzofuran-1-one, Evac-Q-Kwik, Evac-Q-Kit, Evac-U-Gen, component of Correctol, Phenolphthalein (INN), NCGC00018200-07, SMR000059015, Agoral, Fenolftalein [Czech], PHENOLPHTHALEIN [INN], 3,3-bis(4-hydroxyphenyl)-3-hydroisobenzofuran-1-one, Fenolftaleina [INN-Spanish], Phenolphtaleine [INN-French], Phenolphthaleinum [INN-Latin], Phthalide 3,-bis(p-hydroxyphenyl)-, CAS-77-09-8, CCRIS 6266, WLN: T56 BVO DHJ D- D-/R DQ 2, Phenolphthalein (0.04% Solution in Ethanol), HSDB 4161, 1(3H)-Isobenzofuranone, 3-bis(4-hydroxyphenyl)-, EINECS 201-004-7, BRN 0284423, phenolphtalein, UNII-6QK969R2IF, AI3-09081, Phenolphthalein [USP:INN:BAN], FGT, Doxan (Salt/Mix), Agoral (Salt/Mix), Modane (TN), Phenolphthalein White, Laxcaps (Salt/Mix), Phenolphthalein, yellow, Yellow phenolphthalein, Spectrum_001077, Opera_ID_1337, Spectrum2_001279, Spectrum3_000888, Spectrum4_000982, Spectrum5_001268, Modane Plus (Salt/Mix), Phenolphthalein M.P. RS, EC 201-004-7, Phenolphthalein ACS reagent, Phenolphthalein solution R1, PHENOLPHTHALIN [MI], cid_4764, alpha-(p-Hydroxyphenyl)-alpha-(4-oxo-2,5-cyclohexadien-1-ylidene)-o-toluic acid, PHENOLPHTHALEIN [MI], Phenolphthalein, ACS reagent, SCHEMBL27670, BSPBio_002518, KBioGR_001383, KBioSS_001557, Phenolphthalein, pH indicator, PHENOLPHTHALEIN, WHITE, 5-18-04-00188 (Beilstein Handbook Reference), MLS001148397, BIDD:ER0202, DivK1c_000929, PHENOLPHTHALEIN [HSDB], PHENOLPHTHALEIN [IARC], SPECTRUM1500480, Phenolphthalein Paper, DAB 6, SPBio_001278, PHENOLPHTHALEIN [VANDF], orb1311017, PHENOLPHTHALEIN [MART.], PHENPOLPHTHALEIN [VANDF], PHENOLPHTHALEIN [WHO-DD], SCHEMBL29362413, BCBcMAP01_000174, HMS502O11, KBio1_000929, KBio2_001557, KBio2_004125, KBio2_006693, KBio3_001776, NINDS_000929, BP_31, HMS1920H04, HMS2091P06, HMS2236I09, HMS3374P06, HMS5084A18, Pharmakon1600-01500480, component of Correctol (Salt/Mix), HY-D0211, Phenolphthalein, p.a., ACS reagent, Tox21_110838, Tox21_202219, Tox21_300282, BBL002030, BDBM50077844, CCG-39112, EBC-03839, MSK000813, NSC215214, NSC757271, PHENOLPHTHALEIN, WHITE [VANDF], s5395, SBB008868, STK029876, PHENOLPHTHALEIN [EP MONOGRAPH], AKOS000493033, Tox21_110838_1, CS-8152, DB04824, NSC-215214, NSC-757271, IDI1_000929, SMP1_000235, NCGC00018200-01, NCGC00018200-02, NCGC00018200-03, NCGC00018200-04, NCGC00018200-05, NCGC00018200-06, NCGC00018200-08, NCGC00018200-09, NCGC00018200-10, NCGC00018200-12, NCGC00023694-03, NCGC00023694-04, NCGC00023694-05, NCGC00023694-06, NCGC00023694-07, NCGC00254039-01, NCGC00259768-01, AC-14431, BP-30100, ST072636, SY011038, VS-01000, SBI-0051481.P003, EU-0082600, NS00008592, P0094, P0700, P0701, P0702, 3,3-bis(4-hydroxyphenyl)-2-benzofuran-1-on, EN300-92962, Phenolphthalein, SAJ first grade, >=97.0%, .alpha., .alpha.-Di(p-hydroxyphenyl)phthalide, 3,3-bis (4-hydroxyphenyl)-2-benzofuran-1-on, D05456, H12020, Phenolphthalein, JIS special grade, >=98.0%, AB00052070_15, F787639, Q187921, SR-01000000112, SR-01000000112-2, Trihydroxytriphenylmethane-2-carboxylic acid lactone, 3,3-Bis(4-hydroxyphenyl)-2-benzofuran-1(3H)-one #, 3,3-Bis-(4-hydroxy-phenyl)-3H-isobenzofuran-1-one, BRD-K19227686-001-02-0, BRD-K19227686-001-12-9, BRD-K19227686-001-18-6, Z57233591, F0921-4309, Phenolphthalein (263 degrees C) Melting Point Standard, Phenolphthalein, United States Pharmacopeia (USP) Reference Standard, Phenolphthalein Solution R1 according to European Pharmacopoeia 4.1.1, InChI=1/C20H14O4/c21-15-9-5-13(6-10-15)20(14-7-11-16(22)12-8-14)18-4-2-1-3-17(18)19(23)24-20, Phenolphthalein; 2-[Bis(4-hydroxyphenyl)methyl]benzoic acid; 3,3-Bis(4-hydroxyphenyl)phthalide, alpha, alpha.-Di(p-hydroxyphenyl)phthalide;1(3H)-Isobenzofuranone, 3,3-bis(4-hydroxyphenyl)-;1(3H)-Isobenzofuranone,3,3-bis(4-hydroxyphenyl)-;2,2-bis(p-hydroxyphenyl)phthalide;3,3-bis(4-hydroxyphenyl)-1(3h)-isobenzofuranon;alpha-(p-hydroxyphenyl)-alpha-(4-oxo-2,5-cyclohexadien-1-ylidine)-o-toluicacid;alpha-di-(p-hydroxyphenyl)phthalide;alpha-di(p-hydroxyphenyl)phthalide

Phenolphthalein is another weak organic acid. 
Phenolphthalein is not particularly water soluble, so we generally dissolve it in aqueous ethanol. 
The ethanol explains the pleasant, sweet smell of phenolphthalein solutions.

Phenolphthalein is a vital industrial chemical, known for its versatility and essential role in optimizing manufacturing processes. 
Phenolphthalein is integral to applications such as metal treatment, corrosion prevention, and chemical synthesis, ensuring consistent quality and efficiency.
Phenolphthalein is a weak organic acid, at room temperature, appearing as white or microstrip yellow small crystals, being odorless, tasteless, insoluble in water and soluble in alcohol (ethanol) and ether. 

When dissolved in alcohol solution, it can be made of acid and alkali indicator. 
Phenolphthalein is colorless in acid solution while exhibiting red color in the carbonate solution of alkali metal. 
However, if placed in the concentrated alkali solution, it will produce colorless tri-metal Salt so that the red color will fade. 

In view of this feature, laboratory commonly uses it as a kind of acid and alkali titration indicator with the discoloration range of PH being around 8.2 to 10.0, turning from colorless to red. 
When the phenolphthalein reagent is dropped into water or neutral, acidic aqueous solution, there will be white turbidity. 
This is due to that the alcohol is easily soluble in water, so that the reagent water-insoluble phenolphthalein is precipitated out. 

Phenolphthalein is an organic compound widely used as a pH indicator in acid–base titrations.
Phenolphthalein chemical formula is C₂₀H₁₄O₄.
Phenolphthalein is best known for its color change behavior in alkaline solutions.

Chemically, phenolphthalein belongs to the class of phthalein dyes.
Phenolphthalein contains a lactone structure connected to aromatic rings.
Its structure allows reversible structural changes depending on pH.

Physically, phenolphthalein appears as a white to pale yellow crystalline powder.
Phenolphthalein is insoluble in water but soluble in alcohol and alkaline solutions.
In solution, its color depends strongly on pH.

Phenolphthalein exhibits a distinct pH-dependent color change.
Phenolphthalein is colorless in acidic and neutral solutions.
Phenolphthalein turns pink to magenta in mildly alkaline conditions (around pH 8.2–10).

The compound functions through a structural rearrangement mechanism.
In basic solution, the molecule forms a conjugated quinonoid structure.
This extended conjugation produces the characteristic pink color.

Phenolphthalein is chemically stable under dry, controlled conditions.
However, prolonged exposure to light and strong bases may cause degradation.
Proper storage in sealed containers is recommended.

In laboratory chemistry, phenolphthalein is a standard acid–base indicator.
Phenolphthalein is commonly used in titrations involving strong bases.
Its sharp color transition makes it easy to observe.

Historically, Phenolphthalein was used as a laxative, but this use has largely been discontinued due to safety concerns.
Regulatory restrictions apply in many regions.
Phenolphthalein is best described as a pH-sensitive organic indicator dye valued for its clear and reversible color change in alkaline conditions.

Phenolphthalein undergoes a reversible equilibrium between different structural forms depending on pH.
At low pH, it exists in a closed, colorless lactone form.
At higher pH, it converts to an open, conjugated quinonoid form that appears pink.

At very high pH (strongly alkaline conditions), phenolphthalein can become colorless again.
This occurs due to further structural transformation.
This behavior demonstrates its complex acid–base chemistry.

Phenolphthalein has a relatively narrow transition range.
Phenolphthaleins color change typically occurs between pH 8.2 and 10.
This makes it ideal for titrations involving strong bases and weak acids.

The compound is often dissolved in ethanol or alcohol–water mixtures for laboratory use.
Pure water does not dissolve it efficiently.
Alcohol solutions improve clarity and performance as an indicator.

Phenolphthalein is considered a weak acid in chemical terms.
Its ionization in basic solution leads to the colored species.
This acid–base equilibrium underlies its indicator function.

In analytical chemistry, phenolphthalein is sometimes used in alkalinity determination.
Phenolphthalein helps measure carbonate and hydroxide content in water samples.
This application is common in environmental and industrial testing.

The compound exhibits aromatic stability due to its multiple benzene rings.
This contributes to its solid-state stability.
However, it may slowly discolor upon prolonged exposure to air and light.

Phenolphthalein has also been used in demonstration experiments and educational settings.
Its clear and dramatic color change makes it a classic teaching example of acid–base indicators.

Phenolphthalein remains one of the most recognized laboratory indicators worldwide.
Phenolphthalein is a classic, reversible pH indicator with well-characterized chemical behavior and widespread laboratory significance.

Molecular formula: C20H14O4
Molecular weight: 318.32 g/mol
Melting point: 261–263 °C
Boiling point: 417.49 °C (estimate)
Density: 1.27 g/cm3 (32 °C)
Bulk density: 350–450 kg/m3
Vapor pressure: <0.00001 Pa (50 °C)
Refractive index: 1.5400 (estimate)
Flash point: 24 °C
Storage temperature: No restrictions
Solubility: Soluble in alcohol; slightly soluble in ether and DMSO; insoluble in benzene and hexane
Water solubility: <0.1 g/100 mL
Form: Solid
Color: White to yellow-white
Odor: Odorless
pKa: 9.4 (25 °C)
pH: 7.8–10.0
pH range: 8.0 (colorless) – 10.0 (red)
LogP: 2.41
λmax: 552 nm, 553 nm, 374 nm, 276 nm, 229 nm, 205 nm
Colour index: 764
Merck index: 14,7243
BRN: 284423
Stability: Stable; incompatible with strong oxidizing agents and alkalies
InChI: 1S/C20H14O4/c21-15-9-5-13(6-10-15)20(14-7-11-16(22)12-8-14)18-4-2-1-3-17(18)19(23)24-20/h1-12,21-22H
InChIKey: KJFMBFZCATUALV-UHFFFAOYSA-N
SMILES: Oc1ccc(cc1)C2(OC(=O)c3ccccc23)c4ccc(O)cc4

Phenolphthalein mainly acts on the large intestine, which produces semi-liquid excreta in 4 to 8 hours with little or no colic. 
The claim that yellow phenolphthalein is three times stronger than white remains unproven. 
As a result of enterohepatic circulation, the effect of a single dose is sustainable for 3 to 4 days. 

The drug is an active member of many laxatives that can be sold legally without prescription.
Serious adverse effects are rare but can occur when used in excess. 
Phenolphthalein should be avoided on the elderly, because its long-term role can cause severe depletion of water and electrolytes.

Dermatitis (fixed rash, itching, burning sensation, blistering, and residual pigmentation) can occur in allergic patients. 
There were reports of a fatal anaphylaxis but no definite causative relationship with phenolphthalein. 
There are occasional reports of non-thrombocytopenic purpura. 

Long-lasting administration can occasionally caused dehydration and electrolyte imbalance due to excessive diarrhea. 
Phenolphthalein causes alkaline urine or faeces pink.
Phenolphthalein has its chemical name be 2- [bis- (4-hydroxyphenyl) methyl] benzoic acid. 

Phenolphthalein appears as triclinic white to yellowish crystalline powder with the melting point of 237 ~ 259 ℃ and the relative density of 1.277 (20/4 ℃). 
It is easily soluble in ethanol, ether and other organic solvents, slightly soluble in water. 
Phenolphthalein has a weak acidity and is almost completely presented in the molecule state even in very dilute solution. 

Phenolphthalein is soluble in alkaline solution, exhibiting red color in alkaline solution, but is colorless in acidic solution. 
The three benzene rings in the phenolphthalein molecule are linked to the carbon atoms of a sp3 hybrid center, and there is no conjugate relationship between the benzene rings, being colorless. 
After coming across alkali, the lactone ring open and generate disodium salt, the central carbon atoms are transferred into the sp2 hybrid state, containing benzoquinone structure. 

At this time, it forms conjugated system with the three benzene rings which are red; but in excess of alkali, but it is further converted to sp3 hybrid state so that the conjugate system disappears, the color also will recede.
Phenolphthalein is part of a broader group of triphenylmethane derivatives.
Its molecular framework contains three aromatic rings connected to a central carbon atom.

This structure contributes to its conjugation and color-changing properties.
The color change mechanism involves electronic delocalization.
In alkaline solution, electron delocalization increases across the aromatic system.

This extended conjugation shifts light absorption into the visible region, producing the pink color.
Phenolphthalein is commonly prepared by condensation of phthalic anhydride with phenol under acidic conditions.
This reaction forms the characteristic lactone structure.

The synthesis is a classic example of electrophilic aromatic substitution chemistry.
The compound has a melting point around 258–263 °C (decomposition).
Phenolphthalein is thermally stable under normal laboratory conditions.

Decomposition occurs before boiling due to its complex structure.
Phenolphthalein exhibits limited water solubility but high solubility in organic solvents such as ethanol.
This property influences how indicator solutions are prepared.

Alcohol-based solutions are standard in titration practice.
In strongly basic solutions, phenolphthalein can form a colorless carbinol form after the pink stage.
This phenomenon explains why the pink color disappears at very high pH.

Phenolphthalein demonstrates multiple equilibrium states.
Historically, phenolphthalein was used in medical formulations as a stimulant laxative.
However, concerns regarding long-term safety and potential carcinogenic effects led to regulatory withdrawal in many countries.

Its use today is primarily laboratory-based.
Phenolphthalein has also been used in forensic science, particularly in presumptive blood tests (Kastle–Meyer test).
In this application, it reacts in the presence of hemoglobin and hydrogen peroxide to produce a pink color.

This use relies on its redox chemistry rather than its acid–base properties.
Phenolphthalein is recognized as a multifunctional aromatic compound valued for its indicator behavior, synthetic chemistry significance, and historical importance in analytical and forensic science.

Uses Of Phenolphthalein:
Phenolphthalein is one of those chemicals that is commonly used in the chemistry laboratory to tell if a solution is acidic or alkaline.
These chemicals are called acid - base indicators and used as indicator for acidimetric titrations. 
Phenolphthalein exerts laxative effects by stimulating the intestinal mucosa and constricting smooth muscles. 

However, phenolphthalein is no longer used as a laxative due to the suspected carcinogenicity of this compound.
Phenolphthalein can be used as an inhibitor and pH indicator. 
Phenolphthalein also induces centrosome amplification and tubulin depolymerization in vitro.

Phenolphthalein is primarily used as a pH indicator in acid–base titrations.
It is especially suitable for titrations involving strong bases and weak acids.
Its sharp color transition from colorless to pink makes endpoint detection clear.

In alkalinity testing of water, phenolphthalein is used to determine hydroxide and carbonate content.
Phenolphthalein helps assess water quality in environmental and industrial systems.
This application is common in water-treatment analysis.

Phenolphthalein is used in laboratory teaching and demonstration experiments.
Its dramatic color change illustrates acid–base equilibrium concepts.
It is widely used in chemistry education.

In forensic science, phenolphthalein is used in the Kastle–Meyer test for presumptive detection of blood.
It reacts in the presence of hemoglobin and hydrogen peroxide to produce a pink color.
This application relies on its redox behavior.

Phenolphthalein has been used historically as a laxative in pharmaceutical formulations.
However, this use has largely been discontinued due to safety concerns.
Regulatory restrictions now limit its medicinal applications.

In analytical chemistry research, phenolphthalein is used to study acid–base equilibria and indicator behavior.
It serves as a model compound in pH-dependent structural analysis.
Its well-defined transition range supports precise experiments.

Phenolphthalein is also used in quality control testing for alkalinity in industrial processes.
It helps monitor neutralization reactions and base concentration.
This ensures accurate chemical dosing.

Phenolphthalein is used wherever clear visual indication of alkaline conditions or redox activity is required, particularly in laboratory and analytical settings.
Phenolphthalein is used in cement and concrete testing.
It helps detect carbonation in concrete structures by indicating alkaline regions.

Areas that remain pink are alkaline, while colorless areas indicate carbonation.
In food and beverage laboratory analysis, phenolphthalein is used in titration methods to determine acidity or alkalinity.
It supports quality control and formulation monitoring.

This application is analytical rather than as a food additive.
Phenolphthalein is used in pharmaceutical laboratory testing for titration-based assays.
It helps determine the concentration of active ingredients requiring alkaline endpoints.

In chemical manufacturing quality control, phenolphthalein monitors neutralization reactions.
Phenolphthalein confirms when alkaline conditions have been reached.
This helps prevent under- or over-neutralization.

Phenolphthalein is applied in educational chemistry kits and experimental demonstrations.
Phenolphthalein is used in experiments involving invisible ink and acid–base color changes.
Its visual effect makes it popular in teaching environments.

In research on acid–base indicators, phenolphthalein is used as a model compound.
Phenolphthalein s well-characterized transition behavior makes it suitable for studying equilibrium shifts.
This supports analytical method development.

Phenolphthalein may also be used in laboratory calibration of titration equipment.
Phenolphthalein provides a reliable endpoint reference.
Phenolphthalein is used wherever visual detection of alkaline pH, carbonation assessment, or titration endpoint determination is required in laboratory, industrial, and structural analysis contexts.

Safety Profile Of Phenolphthalein:
Human systemic effects: changes in urine composition, gastritis, nausea or vomiting. 
Phenolphthalein is used in medicine as a laxative; in chemistry as an indicator. 
When heated to decomposition it emits acrid smoke and irritating fumes

Phenolphthalein presents moderate health hazards, particularly in powdered or concentrated form.
While commonly used in laboratories, it must be handled with care.
Exposure risks include irritation and potential long-term effects.

Skin contact may cause mild irritation.
Prolonged exposure can result in redness or dryness.
Protective gloves are recommended when handling solid material.

Eye contact can cause irritation and discomfort.
Symptoms may include redness and watering.
Immediate rinsing with water is advised.

Inhalation of dust may cause respiratory irritation.
Coughing or throat discomfort may occur.
Dust generation should be minimized and ventilation used.

Ingestion is harmful and may cause gastrointestinal irritation.
Historically, phenolphthalein was used as a laxative, but high or prolonged doses were linked to potential adverse effects.
Phenolphthalein is no longer widely used in medicine due to safety concerns.

Long-term exposure has been associated with possible carcinogenic risk in animal studies.
Because of this, its pharmaceutical use has been discontinued in many countries.
Regulatory controls limit its consumer applications.