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39-421: Reflecting its slightly hydrophilic character, the white powder is moderately soluble in alcohols and can be recrystallized from hot water. In the presence of a base, it oxidizes readily. The methylated derivatives N -methylaminophenol and N , N -dimethylaminophenol are of commercial value. The compound is one of three isomeric aminophenols, the other two being 2-aminophenol and 3-aminophenol . It

78-467: A change in the proportions of the solvent causing either "compound A" or "impurity B" to precipitate. Hot filtration can be used to separate "compound A" from both "impurity B" and some "insoluble matter C". This technique normally uses a single-solvent system as described above. When both "compound A" and "impurity B" are dissolved in the minimum amount of hot solvent, the solution is filtered to remove "insoluble matter C". This matter may be anything from

117-412: A diluted solution. For a more accurate calculation at a higher concentration, for ionic solutes, Ge and Wang (2010) proposed a new equation: In the above equation, T F is the normal freezing point of the pure solvent (273 K for water, for example); a liq is the activity of the solvent in the solution (water activity for aqueous solution); Δ H T F is the enthalpy change of fusion of

156-402: A minuscule fragment of glass, produced by scratching the side of the glass recrystallization vessel, may provide the nucleus on which crystals may grow. Successful recrystallization depends on finding the right solvent. This is usually a combination of prediction/experience and trial/error. The compounds must be more soluble at higher temperatures than at lower temperatures. Any insoluble impurity

195-489: A mixture of many. These salts are somewhat aggressive to metals, especially iron, so in airports safer media such as sodium formate , potassium formate , sodium acetate , and potassium acetate are used instead. Freezing-point depression is used by some organisms that live in extreme cold. Such creatures have evolved means through which they can produce a high concentration of various compounds such as sorbitol and glycerol . This elevated concentration of solute decreases

234-416: A small amount of "impurity B". There are various possible methods of purification (see Separation process ), recrystallization being one of them. There are also different recrystallization techniques that can be used such as: Typically, the mixture of "compound A" and "impurity B" is dissolved in the smallest amount of hot solvent to fully dissolve the mixture, thus making a saturated solution . The solution

273-511: A solute is determined by comparing m B with the amount of solute dissolved. In this case, i must be known, and the procedure is primarily useful for organic compounds using a nonpolar solvent. Cryoscopy is no longer as common a measurement method as it once was, but it was included in textbooks at the turn of the 20th century. As an example, it was still taught as a useful analytic procedure in Cohen's Practical Organic Chemistry of 1910, in which

312-406: A solute, so that fewer molecules are available to freeze (a lower concentration of solvent exists in a solution versus pure solvent). Re-establishment of equilibrium is achieved at a lower temperature at which the rate of freezing becomes equal to the rate of liquefying. The solute is not occluding or preventing the solvent from solidifying, it is simply diluting it so there is a reduced probability of

351-529: A solvent making an attempt at freezing in any given moment. At the lower freezing point, the vapor pressure of the liquid is equal to the vapor pressure of the corresponding solid, and the chemical potentials of the two phases are equal as well. The phenomenon of freezing-point depression has many practical uses. The radiator fluid in an automobile is a mixture of water and ethylene glycol . The freezing-point depression prevents radiators from freezing in winter. Road salting takes advantage of this effect to lower

390-414: A third impurity compound to fragments of broken glass. For a successful procedure, one must ensure that the filtration apparatus is hot in order to stop the dissolved compounds from crystallizing from the solution during filtration, thus forming crystals on the filter paper or funnel. One way to achieve this is to heat a conical flask containing a small amount of clean solvent on a hot plate. A filter funnel

429-475: A variety of methods, to yield 4-aminophenol. One method involves hydrogenation over a Raney Nickel catalyst . A second method involves selective reduction of the nitro group by Tin(II) Chloride in anhydrous ethanol or ethyl ethanoate . 4-Aminophenol is a building block used in organic chemistry. Prominently, it is the final intermediate in the industrial synthesis of paracetamol . Treating 4-aminophenol with acetic anhydride gives paracetamol: It

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468-441: Is a precursor to amodiaquine , mesalazine , AM404 , parapropamol , B-86810 & B-87836 (c.f. WO 2001042204   ). 4-Aminophenol converts readily to the diazonium salt . Recrystallization (chemistry) In chemistry , recrystallization is a technique used to purify chemicals. By dissolving a mixture of a compound and impurities in an appropriate solvent, the desired compound or impurities can be removed from

507-420: Is added. Examples include adding salt into water (used in ice cream makers and for de-icing roads ), alcohol in water, ethylene or propylene glycol in water (used in antifreeze in cars), adding copper to molten silver (used to make solder that flows at a lower temperature than the silver pieces being joined), or the mixing of two solids such as impurities into a finely powdered drug. In all cases,

546-422: Is also the same principle acting in the melting-point depression observed when the melting point of an impure solid mixture is measured with a melting-point apparatus since melting and freezing points both refer to the liquid-solid phase transition (albeit in different directions). In principle, the boiling-point elevation and the freezing-point depression could be used interchangeably for this purpose. However,

585-413: Is checked after each recrystallization by measuring the melting point, since impurities lower the melting point . NMR spectroscopy can also be used to check the level of impurity. Repeated recrystallization results in some loss of material because of the non-zero solubility of compound A. The crystallization process requires an initiation step, such as the addition of a "seed" crystal. In the laboratory,

624-427: Is dissolve "compound A" and "impurity B" in a suitable solvent at room temperature, filter (to remove insoluble compound/glass), remove the solvent and then recrystallize using any of the methods listed above. Crystallization requires an initiation step. This can be spontaneous or can be done by adding a small amount of the pure compound (a seed crystal ) to the saturated solution, or can be done by simply scratching

663-423: Is produced from phenol by nitration followed by reduction with iron. Alternatively, the partial hydrogenation of nitrobenzene affords phenylhydroxylamine , which rearranges primarily to 4-aminophenol ( Bamberger rearrangement ). It can be produced from nitrobenzene by electrolytic conversion to phenylhydroxylamine , which spontaneously rearranges to 4-aminophenol. 4-nitrophenol can be reduced through

702-412: Is removed by the technique of hot filtration . This method is the same as the above but where two (or more) solvents are used. This relies on both "compound A" and "impurity B" being soluble in a first solvent. A second solvent is slowly added. Either "compound A" or "impurity B" will be insoluble in this solvent and precipitate, whilst the other of "compound A"/"impurity B" will remain in solution. Thus

741-413: Is rested on the mouth, and hot solvent vapors keep the stem warm. Jacketed filter funnels may also be used. The filter paper is preferably fluted, rather than folded into a quarter; this allows quicker filtration, thus less opportunity for the desired compound to cool and crystallize from the solution. Often it is simpler to do the filtration and recrystallization as two independent and separate steps. That

780-413: Is then allowed to cool. As the solution cools the solubility of compounds in the solution drops. This results in the desired compound dropping (recrystallizing) from the solution. The slower the rate of cooling, the bigger the crystals form. In an ideal situation the solubility product of the impurity, B, is not exceeded at any temperature. In that case, the solid crystals will consist of pure A and all

819-400: The cryoscopic constant is larger than the ebullioscopic constant , and the freezing point is often easier to measure with precision, which means measurements using the freezing-point depression are more precise. FPD measurements are also used in the dairy industry to ensure that milk has not had extra water added. Milk with a FPD of over 0.509 °C is considered to be unadulterated. If

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858-420: The molar mass of naphthalene is determined using a Beckmann freezing apparatus . Freezing-point depression can also be used as a purity analysis tool when analyzed by differential scanning calorimetry . The results obtained are in mol%, but the method has its place, where other methods of analysis fail. In the laboratory, lauric acid may be used to investigate the molar mass of an unknown substance via

897-427: The molar mass of the solute. This kind of measurement is called cryoscopy ( Greek cryo = cold, scopos = observe; "observe the cold" ) and relies on exact measurement of the freezing point. The degree of dissociation is measured by determining the van 't Hoff factor i by first determining m B and then comparing it to m solute . In this case, the molar mass of the solute must be known. The molar mass of

936-420: The spring peeper frog ( Pseudacris crucifer ), the molality is increased temporarily as a reaction to cold temperatures. In the case of the peeper frog, freezing temperatures trigger a large-scale breakdown of glycogen in the frog's liver and subsequent release of massive amounts of glucose into the blood. With the formula below, freezing-point depression can be used to measure the degree of dissociation or

975-419: The freezing point of pure water. The freezing point is the temperature at which the liquid solvent and solid solvent are at equilibrium, so that their vapor pressures are equal. When a non-volatile solute is added to a volatile liquid solvent, the solution vapour pressure will be lower than that of the pure solvent. As a result, the solid will reach equilibrium with the solution at a lower temperature than with

1014-435: The freezing point of the ice it is placed on. Lowering the freezing point allows the street ice to melt at lower temperatures, preventing the accumulation of dangerous, slippery ice. Commonly used sodium chloride can depress the freezing point of water to about −21 °C (−6 °F). If the road surface temperature is lower, NaCl becomes ineffective and other salts are used, such as calcium chloride , magnesium chloride or

1053-437: The freezing point of the water inside them, preventing the organism from freezing solid even as the water around them freezes, or as the air around them becomes very cold. Examples of organisms that produce antifreeze compounds include some species of arctic -living fish such as the rainbow smelt , which produces glycerol and other molecules to survive in frozen-over estuaries during the winter months. In other animals, such as

1092-400: The freezing-point depression. The choice of lauric acid is convenient because the melting point of the pure compound is relatively high (43.8 °C). Its cryoscopic constant is 3.9 °C·kg/mol. By melting lauric acid with the unknown substance, allowing it to cool, and recording the temperature at which the mixture freezes, the molar mass of the unknown compound may be determined. This

1131-473: The glass surface to create a seeding surface for crystal growth . It is thought that even dust particles can act as simple seeds. Growing crystals for X-ray crystallography can be difficult. For X-ray analysis, single perfect crystals are required. Typically a small amount (5–100 mg) of a pure compound is used, and crystals are allowed to grow very slowly. Several techniques can be used to grow these perfect crystals: For ice , recrystallization refers to

1170-409: The growth of larger crystals at the expense of smaller ones. Some biological antifreeze proteins have been shown to inhibit this process, and the effect may be relevant in freezing-tolerant organisms. Freezing-point depression Freezing-point depression is a drop in the maximum temperature at which a substance freezes , caused when a smaller amount of another, non- volatile substance

1209-492: The impurities will remain in the solution. The solid crystals are collected by filtration and the filtrate is discarded. If the solubility product of the impurity is exceeded, some of the impurities will co-precipitate. However, because of the relatively low concentration of the impurity, its concentration in the precipitated crystals will be less than its concentration in the original solid. Repeated recrystallization will result in an even purer crystalline precipitate. The purity

4-Aminophenol - Misplaced Pages Continue

1248-447: The proportion of first and second solvents is critical. Typically the second solvent is added slowly until one of the compounds begins to crystallize from the solution and then the solution is cooled. Heating is not required for this technique but can be used. The reverse of this method can be used where a mixture of solvents dissolves both A and B. One of the solvents is then removed by distillation or by an applied vacuum. This results in

1287-567: The pure solvent at T F , which is 333.6 J/g for water at 273 K; Δ C p is the difference between the heat capacities of the liquid and solid phases at T F , which is 2.11 J/(g·K) for water. The solvent activity can be calculated from the Pitzer model or modified TCPC model , which typically requires 3 adjustable parameters. For the TCPC model, these parameters are available for many single salts. The freezing point of ethanol water mixture

1326-411: The pure solvent) acts in opposition to freezing, so that a lower temperature must be reached, over a broader range, before equilibrium between the liquid solution and solid solution phases is achieved. Melting point determinations are commonly exploited in organic chemistry to aid in identifying substances and to ascertain their purity. In the liquid solution, the solvent is diluted by the addition of

1365-423: The pure solvent. This explanation in terms of vapor pressure is equivalent to the argument based on chemical potential, since the chemical potential of a vapor is logarithmically related to pressure. All of the colligative properties result from a lowering of the chemical potential of the solvent in the presence of a solute. This lowering is an entropy effect. The greater randomness of the solution (as compared to

1404-413: The solution is treated as an ideal solution , the extent of freezing-point depression depends only on the solute concentration that can be estimated by a simple linear relationship with the cryoscopic constant (" Blagden 's Law"). where: Some values of the cryoscopic constant K f for selected solvents: The simple relation above doesn't consider the nature of the solute, so it is only effective in

1443-409: The solution, leaving the other behind. The name originates from the crystals often formed when the compound precipitates out. Alternatively, recrystallization can refer to the natural growth of larger ice crystals at the expense of smaller ones. In chemistry , recrystallization is a procedure for purifying compounds . The most typical situation is that a desired "compound A" is contaminated by

1482-401: The substance added/present in smaller amounts is considered the solute , while the original substance present in larger quantity is thought of as the solvent . The resulting liquid solution or solid-solid mixture has a lower freezing point than the pure solvent or solid because the chemical potential of the solvent in the mixture is lower than that of the pure solvent, the difference between

1521-403: The two being proportional to the natural logarithm of the mole fraction . In a similar manner, the chemical potential of the vapor above the solution is lower than that above a pure solvent, which results in boiling-point elevation . Freezing-point depression is what causes sea water (a mixture of salt and other compounds in water) to remain liquid at temperatures below 0 °C (32 °F),

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