CN112285273A - Method for detecting hydroxyl value content of dimethylolpropionic acid - Google Patents
Method for detecting hydroxyl value content of dimethylolpropionic acid Download PDFInfo
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- CN112285273A CN112285273A CN202011278766.8A CN202011278766A CN112285273A CN 112285273 A CN112285273 A CN 112285273A CN 202011278766 A CN202011278766 A CN 202011278766A CN 112285273 A CN112285273 A CN 112285273A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N31/00—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods
- G01N31/16—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods using titration
- G01N31/162—Determining the equivalent point by means of a discontinuity
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/75—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated
- G01N21/77—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator
- G01N21/78—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator producing a change of colour
- G01N21/79—Photometric titration
Abstract
The invention provides a method for detecting the hydroxyl value content of dimethylolpropionic acid, which comprises the following steps: a) mixing acetic anhydride and pyridine, and then shaking up to obtain an acylation reagent; b) dissolving a sample to be detected of dimethylolpropionic acid in the acylation reagent obtained in the step a) to react to obtain a reaction mixed solution; adding a phenolphthalein indicator into the reaction mixed solution, titrating the solution to a terminal point by using an alkali standard solution, and simultaneously carrying out a blank test; and finally, calculating the hydroxyl value content by adopting the following formula: hydroxyl value (mgKOH/g) ═ VAir conditioner‑VSample (A)) C is 56.10/m; in the formula: vAir conditioner-volume of base standard solution consumed at blank drop time, ml; vSample (A)Subtracting the volume of the alkali standard solution consumed by the acid value of the sample to be detected from the volume of the alkali standard solution consumed by the sample at the time of dripping, namely ml; c, concentration of alkali standard solution, mol/l; 56.10 molar mass of potassium hydroxide, g/mol; m is the mass, g, of the sample to be tested of dimethylolpropionic acid.The detection method is simple to operate, simple and convenient to calculate, high in accuracy and good in reproducibility.
Description
Technical Field
The invention relates to the technical field of chemical analysis, in particular to a method for detecting the hydroxyl value content of dimethylolpropionic acid.
Background
Dimethylolpropionic acid is a multipurpose organic raw material and can be used as a chain extender in the preparation of waterborne polyurethane. Dimethylolpropionic acid is a multifunctional hindered dihydric alcohol molecule with both hydroxyl and carboxyl groups, and free acid groups can actively improve the water solubility or the dispersibility of the resin after being neutralized with alkali; polar groups are introduced to improve the adhesion of the coating and the dyeing property of the synthetic fiber; can be applied to water-soluble polyurethane systems, water-soluble alkyd resin and polyester resin, epoxy ester coatings, polyurethane elastomers and powder coatings.
The hydroxyl value of dimethylolpropionic acid is particularly important to detect in the application process, how to accurately detect the hydroxyl value becomes the heaviest, and as dimethylolpropionic acid contains acidic groups and has higher content, the existing hydroxyl value detection mostly adopts acid anhydride to react with hydroxyl, then water is added to hydrolyze the residual acid anhydride, and alkali solution is used for titrating the residual acid content; however, the dimethylolpropionic acid also consumes the alkali solution in the reaction process, so the method for detecting the hydroxyl value content of dimethylolpropionic acid in the prior art has low accuracy and poor reproducibility.
Disclosure of Invention
In view of the above, the invention aims to provide a method for detecting the hydroxyl value content of dimethylolpropionic acid, and the method provided by the invention is simple to operate, simple and convenient to calculate, high in accuracy and good in reproducibility.
The invention provides a method for detecting the hydroxyl value content of dimethylolpropionic acid, which comprises the following steps:
a) mixing acetic anhydride and pyridine, and then shaking up to obtain an acylation reagent;
b) dissolving a sample to be detected of dimethylolpropionic acid in the acylation reagent obtained in the step a) to react to obtain a reaction mixed solution; adding a phenolphthalein indicator into the reaction mixed solution, titrating the solution to a terminal point by using an alkali standard solution, and simultaneously carrying out a blank test; finally, calculating the hydroxyl value content by adopting a formula (I);
hydroxyl value (mgKOH/g) ═ VAir conditioner-VSample (A)) C56.10/m formula (I);
in formula (I):
Vair conditioner-volume of base standard solution consumed at blank drop time, ml;
Vsample (A)Subtracting the volume of the alkali standard solution consumed by the acid value of the sample to be detected from the volume of the alkali standard solution consumed by the sample at the time of dripping, namely ml;
c, concentration of alkali standard solution, mol/l;
56.10 molar mass of potassium hydroxide, g/mol;
m is the mass, g, of the sample to be tested of dimethylolpropionic acid.
Preferably, the volume ratio of acetic anhydride to pyridine in step a) is 1: (8-10).
Preferably, the acylating agent in step a) is stored in a brown bottle, ready for use each time; the acylating agent cannot be used if it turns yellow in color and needs to be reconstituted.
Preferably, the dissolving process in step b) is specifically:
weighing 0.7g to 1.0g of sample to be detected of dimethylolpropionic acid in an iodometry bottle, adding 14ml to 16ml of acylation reagent obtained in the step a), quickly filling a reflux condenser tube, and slowly shaking the iodometry bottle to completely dissolve the sample.
Preferably, the reaction process in step b) is specifically:
immersing an iodine measuring bottle in an oil bath to ensure that the liquid level of the sample is positioned below the oil level of the oil bath, and refluxing for 0.9-1.1 h at 105-115 ℃; taking out the oil level from an iodine measuring flask, adding 5-15 ml of water from the top of a condensation tube, and shaking up; then immersing the iodometry bottle in an oil bath for reaction for 9-11 min, and continuously shaking to obtain a reaction mixed liquid.
Preferably, the phenolphthalein indicator in the step b) is prepared by dissolving pyridine; the concentration of the phenolphthalein indicator is 5g/l to 15 g/l; the addition amount of the phenolphthalein indicator is 5-15 drops.
Preferably, the base standard solution in step b) is 0.5mol/l NaOH standard solution.
Preferably, the preparation and calibration process of the 0.5mol/l NaOH standard solution is as follows:
the preparation process comprises the following steps:
weighing 110g of sodium hydroxide, dissolving in 100ml of carbon dioxide-free water, shaking up, sealing to be clear, taking 27ml of the saturated solution in a 1000ml volumetric flask, and fixing the volume with the carbon dioxide-free water;
the calibration process comprises the following steps:
weighing 3.6g of working reference reagent potassium hydrogen phthalate which is dried in an electric oven at 105-110 ℃ to constant weight, adding 80ml of water without carbon dioxide for dissolution, adding 2d10g/l phenolphthalein indicator, titrating with the prepared sodium hydroxide solution to pink, and keeping for 30 s; simultaneously, performing a blank test;
and (3) calculating: concentration of sodium hydroxide standard solution
In the formula:
m is the exact numerical value of the mass of potassium hydrogen phthalate, g;
v1 — number of volumes of sodium hydroxide solution, ml;
v0 — number of volumes of blank test sodium hydroxide solution, ml;
m is the number of molar masses of potassium hydrogen phthalate, g/mol.
Preferably, the process of titrating to the end point in the step b) is specifically as follows:
titrating to pink by using an alkali standard solution and keeping the color from fading for 25-35 s as an end point.
Preferably, the method further comprises the following steps:
detecting the acid value of a sample to be detected of dimethylolpropionic acid; the process for detecting the acid value of the sample to be detected of the dimethylolpropionic acid specifically comprises the following steps:
weighing 1.0g to 2.0g of dimethylolpropionic acid sample to be detected in a conical flask, adding 20ml to 50ml of toluene-ethanol solution, shaking the conical flask to completely dissolve the sample to be detected, and heating if necessary; adding 10d 10g/L phenolphthalein indicator, titrating to pink with 0.5mol/L potassium hydroxide-ethanol standard titration solution, and keeping the color unchanged for 30s as an end point; simultaneously, performing a blank test;
in the formula (II):
Vsample (A)-volume of base standard solution consumed at the time of sample titration, mL;
Vair conditioner-volume of base standard solution consumed at blank titration, mL;
c, concentration of alkali standard solution, mol/l;
56.10 molar mass of potassium hydroxide, g/mol;
m is the mass, g, of the sample to be tested of dimethylolpropionic acid.
The invention provides a method for detecting the hydroxyl value content of dimethylolpropionic acid, which comprises the following steps: a) mixing acetic anhydride and pyridine, and then shaking up to obtain an acylation reagent; b) dissolving a sample to be detected of dimethylolpropionic acid in the acylation reagent obtained in the step a) to react to obtain a reaction mixed solution; adding a phenolphthalein indicator into the reaction mixed solution, titrating the solution to a terminal point by using an alkali standard solution, and simultaneously carrying out a blank test; and finally, calculating the hydroxyl value content by adopting the following formula: hydroxyl value (mgKOH/g) ═ VAir conditioner-VSample (A)) C is 56.10/m; in the formula: vAir conditioner-volume of base standard solution consumed at blank drop time, ml; vSample (A)-try outSubtracting the volume of the alkali standard solution consumed by the acid value of the sample to be detected of the dimethylolpropionic acid from the volume of the alkali standard solution consumed during the sample dripping; c, concentration of alkali standard solution, mol/l; 56.10 molar mass of potassium hydroxide, g/mol; m is the mass, g, of the sample to be tested of dimethylolpropionic acid. Compared with the prior art, the method has the advantages that the acid anhydride and the dimethylolpropionic acid are fully reacted, the residual acid anhydride is hydrolyzed, then the sodium hydroxide standard solution is used for accurate quantification, and the acid consumption is deducted in the calculation process, so that the hydroxyl value content of the dimethylolpropionic acid is accurately obtained; the detection method provided by the invention is simple to operate, simple and convenient to calculate, high in accuracy and good in reproducibility.
Detailed Description
The technical solutions of the present invention will be described clearly and completely with reference to the following embodiments of the present invention, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention provides a method for detecting the hydroxyl value content of dimethylolpropionic acid, which comprises the following steps:
a) mixing acetic anhydride and pyridine, and then shaking up to obtain an acylation reagent;
b) dissolving a sample to be detected of dimethylolpropionic acid in the acylation reagent obtained in the step a) to react to obtain a reaction mixed solution; adding a phenolphthalein indicator into the reaction mixed solution, titrating the solution to a terminal point by using an alkali standard solution, and simultaneously carrying out a blank test; finally, calculating the hydroxyl value content by adopting a formula (I);
hydroxyl value (mgKOH/g) ═ VAir conditioner-VSample (A)) C56.10/m formula (I);
in formula (I):
Vair conditioner-volume of base standard solution consumed at blank drop time, ml;
Vsample (A)The volume of the alkali standard solution consumed during the dripping of the sample is subtracted by the volume of the alkali standard solution consumed by the acid value of the sample to be detected of dimethylolpropionic acid,ml；
c, concentration of alkali standard solution, mol/l;
56.10 molar mass of potassium hydroxide, g/mol;
m is the mass, g, of the sample to be tested of dimethylolpropionic acid.
Firstly, mixing acetic anhydride and pyridine and then shaking up to obtain the acylation reagent. The source of the acetic anhydride and pyridine in the present invention is not particularly limited, and commercially available products known to those skilled in the art may be used. In the present invention, the volume ratio of acetic anhydride to pyridine is preferably 1: (8-10), more preferably 1: 9.
in the present invention, the acylating agent is preferably stored in a brown bottle, ready for formulation prior to each use; the acylating agent cannot be used if it turns yellow in color and needs to be reconstituted.
After the acylation reagent is obtained, the sample to be tested of the dimethylolpropionic acid is dissolved in the obtained acylation reagent for reaction to obtain a reaction mixed solution. In the invention, the sample to be detected of the dimethylolpropionic acid is a sample to be detected of dimethylolpropionic acid with a known acid value; when the acid value of the sample to be tested of dimethylolpropionic acid is unknown, the method preferably further comprises the following steps:
and detecting the acid value of the sample to be detected of the dimethylolpropionic acid. In the invention, the process for detecting the acid value of the sample to be detected of dimethylolpropionic acid is preferably as follows:
weighing 1.0g to 2.0g of dimethylolpropionic acid sample to be detected in a conical flask, adding 20ml to 50ml of toluene-ethanol solution, shaking the conical flask to completely dissolve the sample to be detected, and heating if necessary; adding 10d 10g/L phenolphthalein indicator, titrating to pink with 0.5mol/L potassium hydroxide-ethanol standard titration solution, and keeping the color unchanged for 30s as an end point; simultaneously, performing a blank test;
in the formula (II):
Vsample (A)-volume of base standard solution consumed at the time of sample titration, mL;
Vair conditioner-volume of base standard solution consumed at blank titration, mL;
c, concentration of alkali standard solution, mol/l;
56.10 molar mass of potassium hydroxide, g/mol;
m is the mass, g, of the sample to be tested of dimethylolpropionic acid.
In the present invention, the standard solution of the base in the formula (II) is a standard titration solution of 0.5mol/L KOH-ethanol.
In the present invention, the dissolving process is preferably specifically:
weighing 0.7-1.0 g of sample to be detected of dimethylolpropionic acid in an iodometry bottle, adding 14-16 ml of acylation reagent obtained in the step a), quickly filling a reflux condenser tube, and slowly shaking the iodometry bottle to completely dissolve the sample;
more preferably:
weighing 0.7g to 1.0g of sample to be detected of dimethylolpropionic acid in an iodine measuring flask, adding 15ml of acylation reagent obtained in the step a), quickly filling a reflux condenser tube, and slowly shaking the iodine measuring flask to completely dissolve the sample.
In the present invention, the dissolution process requires the iodine vial cap to be closed.
In the present invention, the reaction process is preferably specifically:
immersing an iodine measuring bottle in an oil bath to ensure that the liquid level of the sample is positioned below the oil level of the oil bath, and refluxing for 0.9-1.1 h at 105-115 ℃; taking out the oil level from an iodine measuring flask, adding 5-15 ml of water from the top of a condensation tube, and shaking up; then immersing the iodometry bottle in an oil bath for reaction for 9-11 min, and continuously shaking to obtain a reaction mixed solution;
more preferably:
immersing an iodine measuring flask into an oil bath to ensure that the liquid level of the sample is positioned below the oil level of the oil bath, and refluxing for 1h at 105-115 ℃; taking out the oil level from an iodine measuring flask, adding 10ml of water from the top of a condensation tube, and shaking up; then, the iodophor bottle is immersed in an oil bath for reaction for 10min, and is continuously shaken to obtain a reaction mixed solution.
In the present invention, the iodophor is shaken at least twice during the refluxing process.
After the reaction mixed solution is obtained, a phenolphthalein indicator is added into the reaction mixed solution, and an alkali standard solution is used for titration to the end point, and meanwhile, a blank test is carried out. In the invention, the phenolphthalein indicator is preferably prepared by dissolving pyridine; the concentration of the phenolphthalein indicator is preferably 5g/l to 15g/l, and more preferably 10 g/l. In the present invention, the phenolphthalein indicator is preferably added in an amount of 5 to 15 drops, more preferably 10 drops.
In the present invention, the alkali standard solution is preferably 0.5mol/l NaOH standard solution. In the invention, the preparation and calibration process of the 0.5mol/l NaOH standard solution is preferably as follows:
the preparation process comprises the following steps:
weighing 110g of sodium hydroxide, dissolving in 100ml of carbon dioxide-free water, shaking up, sealing to be clear, taking 27ml of the saturated solution in a 1000ml volumetric flask, and fixing the volume with the carbon dioxide-free water;
the calibration process comprises the following steps:
weighing 3.6g of working reference reagent potassium hydrogen phthalate which is dried in an electric oven at the temperature of 105-110 ℃ to constant weight, adding 80ml of water without carbon dioxide for dissolution, adding 2d10g/l of phenolphthalein indicator, titrating with the prepared sodium hydroxide solution until the solution is pink, and keeping the solution for 30 s; simultaneously, performing a blank test;
and (3) calculating: concentration of sodium hydroxide standard solution
In the formula:
m is the exact numerical value of the mass of potassium hydrogen phthalate, g;
v1 — number of volumes of sodium hydroxide solution, ml;
v0 — number of volumes of blank test sodium hydroxide solution, ml;
m is the number of molar masses of potassium hydrogen phthalate, g/mol.
In the present invention, the process of titration to the end point is preferably specifically:
titrating to pink by using an alkali standard solution and keeping the fastness of 25-35 s as an end point;
more preferably:
titration to pink with alkali standard solution and 30s non-fading was kept as the end point.
Finally, the hydroxyl value content is calculated by adopting a formula (I);
hydroxyl value (mgKOH/g) ═ VAir conditioner-VSample (A)) C56.10/m formula (I);
in formula (I):
Vair conditioner-volume of base standard solution consumed at blank drop time, ml;
Vsample (A)Subtracting the volume of the alkali standard solution consumed by the acid value of the sample to be detected from the volume of the alkali standard solution consumed by the sample at the time of dripping, namely ml;
c, concentration of alkali standard solution, mol/l;
56.10 molar mass of potassium hydroxide, g/mol;
m is the mass, g, of the sample to be tested of dimethylolpropionic acid.
In the present invention, V in the formula (I)Sample (A)And subtracting the volume of the alkali standard solution consumed by the acid value of the sample to be detected of the dimethylolpropionic acid from the volume of the alkali standard solution consumed by the sample during the dripping so as to remove the amount of sodium hydroxide consumed by the acid value of the sample to be detected of the dimethylolpropionic acid, namely the amount of alkali liquor consumed by the self acid.
The invention provides a method for detecting the hydroxyl value content of dimethylolpropionic acid, which comprises the following steps: a) mixing acetic anhydride and pyridine, and then shaking up to obtain an acylation reagent; b) dissolving a sample to be detected of dimethylolpropionic acid in the acylation reagent obtained in the step a) to react to obtain a reaction mixed solution; adding a phenolphthalein indicator into the reaction mixed solution, titrating the solution to a terminal point by using an alkali standard solution, and simultaneously carrying out a blank test; and finally, calculating the hydroxyl value content by adopting the following formula: hydroxyl value (mgKOH/g) ═ VAir conditioner-VSample (A)) C is 56.10/m; in the formula: vAir conditioner-volume of base standard solution consumed at blank drop time, ml; vSample (A)Volume-subtracted dihydroxy of base standard solution consumed during sample titrationThe volume of the alkali standard solution consumed by the acid value of the sample to be detected of the methyl propionic acid is ml; c, concentration of alkali standard solution, mol/l; 56.10 molar mass of potassium hydroxide, g/mol; m is the mass, g, of the sample to be tested of dimethylolpropionic acid. Compared with the prior art, the method has the advantages that the acid anhydride and the dimethylolpropionic acid are fully reacted, the residual acid anhydride is hydrolyzed, then the sodium hydroxide standard solution is used for accurate quantification, and the acid consumption is deducted in the calculation process, so that the hydroxyl value content of the dimethylolpropionic acid is accurately obtained; the detection method provided by the invention is simple to operate, simple and convenient to calculate, high in accuracy and good in reproducibility.
To further illustrate the present invention, the following examples are provided for illustration. The reagents used in the following examples of the present invention are all analytical reagents for no particular reason; the laboratory used deionized water.
Example 1
A known batch of dimethylolpropionic acid with an acid number of 470mg (KOH)/g is tested for hydroxyl number.
(1) Preparing an acylation reagent: mixing acetic anhydride and pyridine according to a volume ratio of 1: 9 mixing, shaking the prepared solution evenly, and storing in a brown bottle (the solution is prepared before each use, and cannot be used if the reagent is found to be yellow in color, and needs to be prepared again).
(2) Preparing and calibrating a 0.5mol/l NaOH standard solution:
preparation:
weighing 110g of sodium hydroxide, dissolving in 100ml of carbon dioxide-free water, shaking up, injecting into a polyethylene container, sealing and placing until the solution is clear, measuring 27ml of supernatant by using a plastic tube, placing into a 1000ml volumetric flask, diluting to 1000ml by using carbon dioxide-free water, and shaking up;
calibration:
accurately weighing 3.6g (accurate to 0.0001g) of working reference reagent potassium hydrogen phthalate dried to constant weight in an electric oven at 105-110 ℃, adding 80ml of carbon dioxide-free water for dissolving, adding 2d phenolphthalein indicator (10g/l), titrating by using the prepared sodium hydroxide solution until the solution is pink, and keeping the solution for 30 s; and simultaneously performing a blank test.
And (3) calculating: sodium hydroxide labelConcentration of quasi-solution
In the formula:
m is an accurate value of the mass of potassium hydrogen phthalate in grams (g);
v1 — number of volumes of sodium hydroxide solution in milliliters (ml);
v0 — number of volumes of blank test sodium hydroxide solution in milliliters (ml);
m is the number of molar masses of potassium hydrogen phthalate, in grams per mole (g/mol); m (KHC)8H4O4)＝204.22。
(3) And (3) detection:
weighing 0.7 g-1.0 g of sample to be detected in an iodine measuring flask, adding 15ml of acylation reagent obtained in the step (1), quickly filling a reflux condenser tube, and slowly shaking the iodine measuring flask to completely dissolve the sample; immersing an iodine measuring bottle in an oil bath to ensure that the liquid level of the sample is positioned below the oil level of the oil bath, and refluxing for 1h at the temperature of 110 +/-5 ℃; taking out the iodophor bottle from the oil surface, adding 10ml of water from the top of the condenser tube, and then immersing the iodophor bottle in an oil bath for reaction for 10min while continuously shaking; taking out the reflux device, cooling to room temperature, and adding 15ml of n-butanol from the top of the condensation tube to flush the condensation tube; adding 10 drops of 10g/l phenolphthalein indicator, titrating to pink by using 0.5mol/l NaOH standard solution obtained in the step (2), and keeping the fading of 30s as an end point; and simultaneously performing a blank test.
Hydroxyl value (mgKOH/g) ═ VAir conditioner-VSample (A)) C56.10/m formula (I);
in formula (I):
Vair conditioner-volume of base standard solution consumed at blank drop time, ml;
Vsample (A)The volume of base standard solution consumed at the time of sample titration (volume of sodium hydroxide standard solution consumed minus the corresponding mass of acid number), ml;
c, concentration of alkali standard solution, mol/l;
56.10 molar mass of potassium hydroxide, g/mol;
m-mass of sample, g.
TABLE 1 Experimental data for the method of determining the hydroxyl number content of dimethylolpropionic acid provided in example 1
Example 2
The hydroxyl value content of the existing batch of dimethylolpropionic acid of which the acid value is unknown needs to be detected.
(1) Preparing an acylation reagent: mixing acetic anhydride and pyridine according to a volume ratio of 1: 9 mixing, shaking the prepared solution evenly, and storing in a brown bottle (the solution is prepared before each use, and cannot be used if the reagent is found to be yellow in color, and needs to be prepared again).
(2) Preparing and calibrating a 0.5mol/l NaOH standard solution:
preparation:
weighing 110g of sodium hydroxide, dissolving in 100ml of carbon dioxide-free water, shaking up, injecting into a polyethylene container, sealing and placing until the solution is clear, measuring 27ml of supernatant by using a plastic tube, placing into a 1000ml volumetric flask, diluting to 1000ml by using carbon dioxide-free water, and shaking up;
calibration:
accurately weighing 3.6g (accurate to 0.0001g) of working reference reagent potassium hydrogen phthalate dried to constant weight in an electric oven at 105-110 ℃, adding 80ml of carbon dioxide-free water for dissolving, adding 2d phenolphthalein indicator (10g/l), titrating by using the prepared sodium hydroxide solution until the solution is pink, and keeping the solution for 30 s; and simultaneously performing a blank test.
And (3) calculating: concentration of sodium hydroxide standard solution
In the formula:
m is an accurate value of the mass of potassium hydrogen phthalate in grams (g);
v1 — number of volumes of sodium hydroxide solution in milliliters (ml);
v0 — number of volumes of blank test sodium hydroxide solution in milliliters (ml);
m is the number of molar masses of potassium hydrogen phthalate, in grams per mole (g/mol); m (KHC)8H4O4)＝204.22。
(3) And (3) detection:
firstly, detecting the acid value of a sample to be detected:
weighing 1.0g to 2.0g of a sample to be detected in a conical flask, adding 20ml to 50ml of toluene-ethanol solution, shaking the conical flask to completely dissolve the sample to be detected, and heating if necessary; adding 10d 10g/L phenolphthalein indicator, titrating to pink with 0.5mol/L potassium hydroxide-ethanol standard titration solution, and keeping the color from fading for 30s as an end point; and simultaneously performing a blank test.
In the formula (II):
Vsample (A)-volume of base standard solution consumed at the time of sample titration, mL;
Vair conditioner-volume of base standard solution consumed at blank titration, mL;
c, concentration of alkali standard solution, mol/l;
56.10 molar mass of potassium hydroxide, g/mol;
m-mass of sample, g.
TABLE 2 Experimental data for the determination of the acid number content of dimethylolpropionic acid in example 2
And (3) detecting a hydroxyl value:
weighing 0.7 g-1.0 g of sample to be detected in an iodine measuring flask, adding 15ml of acylation reagent obtained in the step (1), quickly filling a reflux condenser tube, and slowly shaking the iodine measuring flask to completely dissolve the sample; immersing an iodine measuring bottle in an oil bath to ensure that the liquid level of the sample is positioned below the oil level of the oil bath, and refluxing for 1h at the temperature of 110 +/-5 ℃; taking out the iodophor bottle from the oil surface, adding 10ml of water from the top of the condenser tube, and then immersing the iodophor bottle in an oil bath for reaction for 10min while continuously shaking; taking out the reflux device, cooling to room temperature, and adding 15ml of n-butanol from the top of the condensation tube to flush the condensation tube; adding 10 drops of 10g/l phenolphthalein indicator, titrating to pink by using 0.5mol/l NaOH standard solution obtained in the step (2), and keeping the fading of 30s as an end point; and simultaneously performing a blank test.
Hydroxyl value (mgKOH/g) ═ VAir conditioner-VSample (A)) C56.10/m formula (I);
in formula (I):
Vair conditioner-volume of base standard solution consumed at blank drop time, ml;
Vsample (A)The volume of base standard solution consumed at the time of sample titration (volume of sodium hydroxide standard solution consumed minus the corresponding mass of acid number), ml;
c, concentration of alkali standard solution, mol/l;
56.10 molar mass of potassium hydroxide, g/mol;
m-mass of sample, g.
TABLE 3 Experimental data of the method for determining the hydroxyl value content of dimethylolpropionic acid provided in example 2
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (10)
1. A method for detecting the hydroxyl value content of dimethylolpropionic acid comprises the following steps:
a) mixing acetic anhydride and pyridine, and then shaking up to obtain an acylation reagent;
b) dissolving a sample to be detected of dimethylolpropionic acid in the acylation reagent obtained in the step a) to react to obtain a reaction mixed solution; adding a phenolphthalein indicator into the reaction mixed solution, titrating the solution to a terminal point by using an alkali standard solution, and simultaneously carrying out a blank test; finally, calculating the hydroxyl value content by adopting a formula (I);
hydroxyl value (mgKOH/g) ═ VAir conditioner-VSample (A)) C56.10/m formula (I);
in formula (I):
Vair conditioner-volume of base standard solution consumed at blank drop time, ml;
Vsample (A)Subtracting the volume of the alkali standard solution consumed by the acid value of the sample to be detected from the volume of the alkali standard solution consumed by the sample at the time of dripping, namely ml;
c, concentration of alkali standard solution, mol/l;
56.10 molar mass of potassium hydroxide, g/mol;
m is the mass, g, of the sample to be tested of dimethylolpropionic acid.
2. The detection method according to claim 1, wherein the volume ratio of acetic anhydride to pyridine in step a) is 1: (8-10).
3. The assay of claim 1 wherein the acylating reagent of step a) is stored in a brown bottle and is dispensed prior to each use; the acylating agent cannot be used if it turns yellow in color and needs to be reconstituted.
4. The detection method according to claim 1, wherein the dissolution process in step b) is specifically:
weighing 0.7g to 1.0g of sample to be detected of dimethylolpropionic acid in an iodometry bottle, adding 14ml to 16ml of acylation reagent obtained in the step a), quickly filling a reflux condenser tube, and slowly shaking the iodometry bottle to completely dissolve the sample.
5. The detection method according to claim 4, wherein the reaction in step b) is specifically carried out by:
immersing an iodine measuring bottle in an oil bath to ensure that the liquid level of the sample is positioned below the oil level of the oil bath, and refluxing for 0.9-1.1 h at 105-115 ℃; taking out the oil level from an iodine measuring flask, adding 5-15 ml of water from the top of a condensation tube, and shaking up; then immersing the iodometry bottle in an oil bath for reaction for 9-11 min, and continuously shaking to obtain a reaction mixed liquid.
6. The detection method according to claim 1, wherein the phenolphthalein indicator in step b) is prepared by dissolving pyridine; the concentration of the phenolphthalein indicator is 5g/l to 15 g/l; the addition amount of the phenolphthalein indicator is 5-15 drops.
7. The detection method according to claim 1, wherein the alkali standard solution in step b) is 0.5mol/l NaOH standard solution.
8. The detection method according to claim 7, wherein the preparation and calibration process of the 0.5mol/l NaOH standard solution is specifically as follows:
the preparation process comprises the following steps:
weighing 110g of sodium hydroxide, dissolving in 100ml of carbon dioxide-free water, shaking up, sealing to be clear, taking 27ml of the saturated solution in a 1000ml volumetric flask, and fixing the volume with the carbon dioxide-free water;
the calibration process comprises the following steps:
weighing 3.6g of working reference reagent potassium hydrogen phthalate which is dried in an electric oven at the temperature of 105-110 ℃ to constant weight, adding 80ml of water without carbon dioxide for dissolution, adding 2d10g/l of phenolphthalein indicator, titrating with the prepared sodium hydroxide solution until the solution is pink, and keeping the solution for 30 s; simultaneously, performing a blank test;
and (3) calculating: concentration of sodium hydroxide standard solution
In the formula:
m is the exact numerical value of the mass of potassium hydrogen phthalate, g;
v1 — number of volumes of sodium hydroxide solution, ml;
v0 — number of volumes of blank test sodium hydroxide solution, ml;
m is the number of molar masses of potassium hydrogen phthalate, g/mol.
9. The detection method according to claim 1, wherein the titration to the end point in step b) is specifically performed by:
titrating to pink by using an alkali standard solution and keeping the color from fading for 25-35 s as an end point.
10. The detection method according to any one of claims 1 to 9, further comprising:
detecting the acid value of a sample to be detected of dimethylolpropionic acid; the process for detecting the acid value of the sample to be detected of the dimethylolpropionic acid specifically comprises the following steps:
weighing 1.0g to 2.0g of dimethylolpropionic acid sample to be detected in a conical flask, adding 20ml to 50ml of toluene-ethanol solution, shaking the conical flask to completely dissolve the sample to be detected, and heating if necessary; adding 10d 10g/L phenolphthalein indicator, titrating to pink with 0.5mol/L potassium hydroxide-ethanol standard titration solution, and keeping the color unchanged for 30s as an end point; simultaneously, performing a blank test;
in the formula (II):
Vsample (A)-volume of base standard solution consumed at the time of sample titration, mL;
Vair conditionerBlank drop timing mechanismThe volume of the base standard solution, mL, was consumed;
c, concentration of alkali standard solution, mol/l;
56.10 molar mass of potassium hydroxide, g/mol;
m is the mass, g, of the sample to be tested of dimethylolpropionic acid.
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