Phthalic anhydride resorcinol. Physicochemical methods for the determination of phenol. Obtaining from chlorobenzene

Organic matter from the group of phenols, a simple dihydric phenol. Among chemists, the names resorcinol and 1,3-dihydroxybenzene are also used. The formula of resorcinol is similar to the formulas of hydroquinone and pyrocatechol, the difference is in the structure of the molecule; in how the OH groups are attached.

Properties

The substance is colorless needle crystals or a white crystalline powder with a pungent phenolic odor. Sometimes the powder can be pinkish or yellowish. If it is strongly colored, turns pink-orange or brown, it means that the reagent was stored incorrectly and it has oxidized. Resorcinol is fire hazardous. It dissolves well in water, diethyl ether, ethyl alcohol, acetone. Can be dissolved in oils, glycerin. Almost insoluble in chloroform, carbon disulfide, benzene.

The reagent exhibits Chemical properties phenols. Strong reducing agent, easily oxidized. Reacts with alkalis to form phenolate salts; with ammonia, halogens, with strong acids(for example, with nitrogen, sulfuric, picrine, glacial acetic acid).

For the qualitative determination of resorcinol, the following reactions are used:
- with ferric chloride - the solution turns into a deep purple, almost black color;
- fusion with phthalic anhydride in the presence of a catalyst leads to the formation of a characteristically colored, fluorescent green substance - fluorescein. The fluorescein itself has a yellow-red color of the solution (the reaction distinguishes resorcinol from other phenols).

Dust of resorcinol and especially its vapors irritate the skin, respiratory organs, mucous membranes of the eyes. Inhalation of vapors and dust of the reagent causes coughing, nausea, heart palpitations, dizziness, so you need to work with resorcinol using respirators or masks, goggles, in overalls, in a ventilated room. If you suspect poisoning, you need to rinse the site of exposure to the reagent with plenty of water, take the victim to fresh air, call a doctor.

Store resorcinol in an airtight container, in dark, dry, cool rooms, strictly separate from flammable substances.

Application

Resorcinol is in demand in the chemical industry as a raw material for the production of artificial colors, fluorescein, resorcinol-formaldehyde resins, solvents, stabilizers, plasticizers and UV absorbers for plastics.
- V analytical chemistry used in colorimetric studies. With its help, the content of zinc, lead, carbohydrates, furfural, lignin, etc. is determined.
- In the rubber industry.
- In the fur industry, as a dye for furs.
- It is widely used in medicine and pharmaceuticals. It is used as a disinfectant, cauterizing agent, wound healing agent, and antihelmintic. It is part of solutions and ointments for the treatment of various, including fungal and purulent, skin diseases; acne, seborrhea, dermatitis, eczema, age spots.
- To obtain explosives.

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Fluorescein synthesis

I decided to experiment with fluorescein, but there was no ready-made reagent at hand: I had to conduct a trial synthesis. Phthalic anhydride and a few grams of resorcinol were available. I took the methodology from the article as a basis.

For a trial experiment, he did not calculate the required amounts of substances: he simply took 1 g of phthalic anhydride, 1 g of resorcinol, mixed. The mixture was placed in a 50 ml beaker and moistened with about 0.5 ml of concentrated sulfuric acid.

The glass is fixed over the included electric stove. The mixture melted and turned crimson. Later - reddish brown. He controlled the heating, then removing, then substituting tiles under the glass. In general, the mixture boiled slightly for about 5 minutes. When the glass was removed from the hotplate, phthalic anhydride needles formed in the upper part of it.

I prepared a solution of 0.5 g of sodium hydroxide in 50 ml of water. The mixture had to be poured from a glass into an alkali solution, without allowing it to cool - otherwise it would solidify. In the case of the test tube (see the cited article), this was apparently not difficult, but the glass has a larger surface - the mixture solidified. From the glass, only a few drops were poured into the alkali solution, which froze at the bottom in the form of green balls. The solution turned yellowish-green with characteristic fluorescence.

The rest of the frozen melt was problematic to get out of the glass. I decided: "If the mountain does not go to Mohammed, it is not a sin to go to the mountain." Instead of trying to whip out the product to transfer it to the alkali, it is better to pour the alkali into a glass with the frozen reaction mixture and wait until it dissolves.

The result is a dark green liquid with sediment. He put the glass on the switched off, but still hot stove. The reaction mixture gradually lagged behind the walls, and the liquid turned brown.

So I left it for the weekend. Then he was also worried that the glass had to be covered so that fluorescein in an alkaline medium would not be oxidized by air (I did not meet any indications of such a danger in the literature, but who knows ...)

After the weekend, I came to work and looked at my fluorescein (on Friday I left a glass with a melt, filled with a solution of alkali on a cooling tile).

The glass contained a yellow solution (sodium salt of fluorescein - uranine) and a red powder - fluorescein precipitate. However, not all of the precipitate was in powder form. A mass similar to caramel (undissolved melt) adhered to the glass rod.

The contents of the glass was filtered: a yellow solution formed, and a red precipitate settled on the filter.

When I looked at the method of obtaining fluorescein from resorcinol and phthalic anhydride, I was convinced that I took phthalic anhydride in excess (22.5 g of resorcinol needed 15 g of phthalic anhydride, but I took at random: 1 g of resorcinol - 1 g of phthalic anhydride).

That is why not all the melt dissolved, the medium in the glass was clearly not alkaline, and most of the fluorescein was in the precipitate (remember: fluorescein is slightly soluble in water, and its sodium salt [uranine] is much better).

The stick with the mass adhered to it was transferred into a clean glass, added caustic soda granules and a little water. The melt gradually dissolved, forming a red-brown opaque solution. Later, to the fluorescein that remained on the filter, I added alkali and also transferred it into solution. The solutions are combined.

(By and large, it was not necessary to filter out fluorescein: it was enough to drain the liquid from the precipitate as much as possible, and add alkali to the resulting suspension. further experiments are of great importance does not).

A drop of the brown solution was added to a three-liter jar of water. The drop gradually descended, forming vortex rings, filaments and "clouds". At first, the drop was brown, then gradually turned yellow-green with distinct fluorescence. Indescribable beauty. Later, a similar experiment was carried out in a five-liter jar.

So let's start experimenting with fluorescein.

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Complexation reaction with iron (III) ions

It is based on the properties of phenolic hydroxyl to form soluble complex compounds, often colored blue (phenol) or violet (resorcinol, salicylic acid), less often red (PASK - sodium) and green (quinosol, adrenaline).

The composition of the complexes, and, consequently, their color is determined by the amount of phenolic hydroxyls, the influence of other functional groups, and the reaction of the medium.

Resorcinol

The reaction of the formation of oxyazo compounds.

This is a very sensitive color reaction.

The azo coupling can also take place in the o-position with respect to the phenolic hydroxyl. Resorcinol forms the dye resorcinol yellow:

Lieberman's reaction. The reaction is carried out by fusing crystals of resorcinol and nitroso compound. Then add concentrated sulfuric acid A violet color appears.

Oxidation reactions. When phenols are oxidized, a mixture of colored substances is obtained. So, when exposed to hypochlorites or bromic water in the presence of ammonia, quinones, quinoneimines, and indophenols are formed.

Resorcinol - brownish yellow

Condensation reactions. When resorcinol is fused with phthalic anhydride (or with potassium hydrogen phthalate), a yellow-red melt is formed:

When the melt dissolves in a sodium hydroxide solution, intense green fluorescence appears (due to the formation of a quinoid cycle in the molecule):

When phthalic anhydride interacts with phenol, phenolphthalein is formed, which has a purple color in an alkaline medium, and thymol forms thymolphthalein, which acquires a blue color under the same conditions.

Substitution reactions (with bromic water and nitric acid)

The reactions are based on the ability of phenols to brominate and nitrate by replacing a mobile hydrogen atom in the ortho and para positions.

Bromo derivatives precipitate white, and nitro derivatives are yellow.

resorcinol white precipitate

yellow coloration

GOUVPO PENZA STATE UNIVERSITY

Medical Institute

Specialty "Pharmacy"

Final interdisciplinary exam

Examination ticket number 11

1. Pharmaceutical enterprises and pharmacies receive medicinal plant raw materials harvested from the plant Arctostaphyllosuva-ursi (L.) Spreng., Family. Ericaceae.

During the analytical control of the quality criteria of raw materials, it was found that the content of active substances in the raw materials was 8%; humidity 10.5%; total ash 3.3%; ash insoluble in 10% hydrochloric acid solution 1%; browned and darkened leaves 2%; other parts of the plant (twigs, fruits) 4%, organic impurities 0.2%; mineral impurity 0.1%.

Analyze the results obtained and make a conclusion about the quality of raw materials and the possibility of their further use. Explain your decision.

Give brief description plant and raw materials. What life form does the plant have, where does it grow (range, habitat), what are the features of collecting raw materials?

Please indicate chemical composition raw materials and the formula of the main active ingredient. What class of substances does it belong to? Explain what physical and chemical properties of active ingredients are used in pharmacopoeial methods of qualitative and quantitative natural definition.

What pharmacological group does the raw material belong to? What drugs are obtained from raw materials?

2. When assessing the quality of substance "3", it was noted that in samples of one batch of its appearance did not meet the requirements of ND for the section "Description" - the samples were damp and dirty pink.

Give justification for the reasons for the change in its quality for this indicator in accordance with with properties and give other tests characterizing the quality of this medicinal substances:

Give the Russian, Latin and rational name of the drug. Describe the physical and chemical properties (appearance, solubility, spectral and optical characteristics) and sludge use for quality assessment.

According to the chemical properties, suggest reactionsidentification and quantification methods. Writethose reaction equations.

Phenols

Acidic properties

Phenols are much more acidic than alcohols and water, but they are weaker than carbonic and carboxylic acids and do not stain litmus.

The pKa values ​​are as follows: phenol - 9.89, acetic acid - 4.76, carbonic acid - 6.12.

The more stable the anion, the stronger the acid.

Restorative properties

Phenols are easily oxidized even by atmospheric oxygen, thereforeduring storage, the appearance of shades is possible(pink, yellow go, brown ).

O- Benzoquinone

Diatomic phenols oxidize faster than monohydric phenols... The oxidation rate also depends on the pH of the medium. In an alkaline environment, oxidation is faster. Due to the ease of oxidation of pharmaco peya introduces indicator: chromaticity . esorcinol is oxidized to form a mixture of products,but without m-quinones.

Phenols dissolve well in aqueous solutions of alkalis withformation of phenolates however, this reaction cannot be used for quantitative determination due to hydrolysis of the resulting salt.

Phenols do not interact with hydrocarbons alkali metals, because they are weaker than carbonic acid and cannot displace it. Phenols and carboxylic acids are distinguished by the reaction of interaction with alkali metal bicarbonates.

A characteristic qualitative reaction to phenols is the formation of colored complexes [ Fe ( OR ) 6 ] 3 ~ with salts of three tape iron ... The color depends on the number of hydroxyl groups, their location, and the presence of other functional groups.

Coloring of complexes of phenol derivatives and iron (III) chloride

Halogenation

With an excess of bromine water, a yellow 2,4,4,6-tetra-bromocyclohexadien-2,5-one is formed:

The halogenation of phenols proceeds most easily in an alkaline medium, but phenol is oxidized in a strongly alkaline medium. Resorcinol is brominated in an acidic medium, forming tribromresorcinol, which is soluble in water. If one of the positions is occupied (like thymol), a dibromo derivative is formed:

Halogenation reactions are also used for quantitativedetermination of phenols
. Nitrosation (Lieberman's nitrosoreaction)

An authenticity reaction such as an indophenol test is based on the ability of drugs to oxidize. As an oxidizing agent use bleach, chloramine, bromine water:

Reactions are blown in easily if O- and n-positions are not occupied.

Electrophilic substitution reactions

The hydroxyl group associated with the aromatic nucleus in an alkaline solution is the strongest ortho- and para-orientant. In this regard, reactions are easy for phenols. halogenation, nitroasting, nitration, etc..

The nitroso group enhances the hydrogen mobility of the phenolichydroxyl, isomerization occurs. Emerging quinone oxime condenses with phenol:

Data on the color of the indophenols formed during Lieberman's nitrosoreaction are presented in table.

Table 37. Coloring of indophenols (obtained by nitrosation)

Nitration

Phenols are nitrated with nitric acid, diluted at room temperature, with educationO- and p-nitrophenol:

Adding solution sodium hydroxide enhances coloration due to the formation of a well-dissociated salt:

The reaction of the combination of phenols with a diazonium salt in an alkaline medium

Phenols readily enter into a substitution reaction with diazonium salts in an alkaline medium with the formation of azo dyes, which in this medium have a color from orange to cherry red:

This is a common reaction to phenols that do not have substituents in the ortho and para positions. The easier combination occurs in the para position due to the formation of a long chain of conjugated bonds.

Due to instability, the diazonium salt is prepared immediately before the reaction, using compounds with a primary aromatic amino group:

When an azo dye is formed, the pH of the medium should not be higher than 9.0-10.0, since in a strongly alkaline medium, the diazonium salt forms a diazohydrate that is not capable of azo coupling:

^ DiazohydrateOxidation and condensation reactions

The formation of arylmethane dyes occurs during the condensation of phenols with an aldehyde

Arylmethanedye(redcolors

For thymol, a condensation reaction with chloroform in an alkaline medium is proposed. The reaction product is colored red-violet:

For phenols with a free p-position, a condensation reaction with 2,6-dichloroquinonechlorimide is characteristic, while indophenol is formed:

The formation of an indophenol derivative is possible by nitration of thymol in the medium of acetic anhydride and concentrated sulfuric acid:

Reactions of condensation of phenols with lactones (phthalic anhydride) are often used. With phenol, the condensation product is called phenolphthalein and is used as an indicator that hasIn the local environment, raspberry color:

Thymol forms thymolphthalein - an indicator coloredin an alkaline environment in blue:

Resorcinol fusion in a porcelain crucible with an excess of phthalic anhydride in the presence of a few drops of concentratedH 2 S0 4 ... The resulting melt yellow-red after cooling, it is poured into a dilute alkali solution. Appears intensively green fluorescence of the fluorescein formed as a result of the reaction:

Purity analysis

V resorcinol determine the impuritypyrocatechol by reaction with ammonium with molybdate. In the presence of an impurity color appears, the intensity of which compare with the reference.

Another impurity in the preparation resorcinol -phenol . The phenol impurity is determined by smell, for this a preparation with a small amount water is heated in a water bath at a temperature of 40-50 ° C.

V thymole determine the impurityphenol by reaction with iron (III) chloride. By the condition of the GF methodology concentration thymol due to its low solubility is 0.085%. Coloration complex of thymol with iron chloride at this concentration not res accepted, and if there isphenol impurities appears violet I am coloring. The admixture of phenol in the preparation is unacceptable.

quantitation

For quantitative determination of phenols is usedbromatometry: as straight(thymol), and reverse (phenol, resor-

qing, sinestrol) method. A preparation, an excess of a titrated solution of potassium bromate and potassium bromide is placed in a bottle with a ground stopper. Acidified with sulfuric acid:

The reaction takes place within 10-15 minutes; for this time, the bottle is left in a dark place. Then a solution of potassium iodide is added to the mixture and left for another 5 minutes:

Direct titration accepted by the GF for quantitative determination thymol. In direct titration, an excess drop of iodine changes the color of the indicators (methyl orange, methyl redleg). V back titration the released iodine is titrated with a solution sodium thiosulfate. Indicator - starch.

It should be remembered that the bromination process is influenced by the conditions of determination: the duration of the reaction, the concentration of the acid.

Molar mass equivalents, denoted asM(l/ z) followdying:

phenol-1/6,

resorcinol-1/6,

thymol-1/4,

In the opposite way, a control experiment must be carried out..

Resorcinol

Qualitative reactions

1. A solution of resorcinol from 1 drop of a solution of ferric chloride takes on different shades of blue to dark purple, color.

2. On careful heating of 0.5 g of resorcinol with 0.1 g of tartaric acid and strong sulfuric acid, a dark carmine-red color appears.

3. When resorcinol is heated with phthalic anhydride, fluorescein is formed:

4. When several milliliters of a 2% solution of resorcinol are heated in a caustic alkali solution in a water bath and a few drops of chloroform (or chloral hydrate solution) are added, the mixture turns into an intense red color (unlike hydroquinone and pyrocatechol), turning into yellowish after acidification diluted acetic acid.

5. Bromine water releases sediment - see Quantification.

quantitation

The bromometric determination is based on the fact that bromine in excess interacts with resorcinol to form tribromoresorcinol:

Excess bromine is determined iodometrically.

Dissolve 1 g of resorcinol in water in a 100 ml volumetric flask and make up to the mark. 25 ml of this solution is poured into a 500 ml bottle with a ground stopper, 50 ml of bromate-bromide mixture (2.7833 g of potassium bromate and 50 g of potassium bromide in 1 liter of solution), 50 ml of water, 5 ml of hydrochloric acid ( sp. weight 1.15) and leave for one minute, after which another 20 ml of water and 1 g of potassium iodide are added. The liquid is left for 5 minutes and the released iodine is titrated with 0.1 N. sodium thiosulfate solution (indicator - starch solution). 1 ml 0.1 N. potassium bromate solution corresponds to 0.001835 g of resorcinol.