Citric acid

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Citric acid
Citric acid.jpg
Food grade citric acid.
Citric acid.png
Names
IUPAC name
3-carboxy-3-hydroxypentane-1,5-dioic acid
Systematic IUPAC name
Citric acid
Other names
3-carboxy-3-hydroxypentanedioic acid
2-hydroxy-1,2,3-propanetricarboxylic acid
Identifiers
Jmol-3D images Image
Properties
C6H8O7
Molar mass 192.12 g/mol
Appearance slightly hygroscopic colorless solid
Odor Odorless
Density 1.665 g/cm3 (anhydrous)
1.542 g/cm3 (monohydrate, at 18 °C)
Melting point 156 °C (313 °F; 429 K) (decomposes)
Boiling point 310 °C (590 °F; 583 K) (decomposes from 175 °C)
117.43 g/100 mL (10 °C)
147.76 g/100 mL (20 °C)
180.89 g/100 mL (30 °C)
220.19 g/100 mL (40 °C)
382.48 g/100 mL (80 °C)
547.79 g/100 mL (100 °C)
Solubility Soluble in ethanol, diethyl ether, ethyl acetate, DMSO, methanol
Insoluble in benzene, carbon disulfide, chloroform, toluene, xylene
Solubility in ethanol 62 g/100 g (25 °C)
Solubility in amyl acetate 4.41 g/100 g (25 °C)
Solubility in diethyl ether 1.05 g/100 g (25 °C)
Solubility in 1,4-Dioxane 35.9 g/100 g (25 °C)
Acidity (pKa) pKa1 = 3.13
pKa2 = 4.76
pKa3 = 6.39, 6.40
Viscosity 6.5 cP (50% aq. sol.)
Thermochemistry
252.1 J/(mol·K)
-1548.8 kJ/mol
Hazards
Safety data sheet ScienceLab
Flash point 155
Lethal dose or concentration (LD, LC):
3000 mg/kg (rats, oral)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Citric acid or 2-hydroxy-1,2,3-propanetricarboxylic acid (IUPAC name 2-hydroxypropane-1,2,3-tricarboxylic acid) is a weak organic acid, mostly used in the food industry, where it serves as a preservative and a food additive that gives a pleasant sour taste. It has the chemical formula C6H8O7.

Properties

Chemical

Citric acid will react in solution with bases, carbonates and bicarbonates, as well as reactive metals, such as magnesium, to form their respective salts, citrates.

Mg + C6H8O7 → C6H6O7Mg + H2

As can be seen with its use as a preservative for fruits, it often serves as a reducing agent, similar to ascorbic acid, both in nature and some syntheses.

Citric acid has a hydroxyl group, with which it can form some mineral acid esters. It also may be used in the production of some exotic polyesters.

Physical

Citric acid is at standard conditions a white hygroscopic crystalline powder. It exists either in an anhydrous (water-free) form or as a monohydrate. The monohydrate can be converted to the anhydrous form by heating above 78 °C. It is soluble in water, ethanol, diethyl ether, ethyl acetate, DMSO and insoluble in benzene, toluene, chloroform, carbon disulfide.

Availability

Citric acid is available in stores as lemon salt, either pure or mixed with other additives. It can be found in pickling and canning sections of grocery stores already in pure, food-grade form.

Williams-Sonoma sells citric acid in small glass jars.

Legal

While not controlled, there were some reports in the past years of law enforcement agencies monitoring the purchase of large amounts of citric acid, mainly due to its use in the production of HMTD. Some drug users use citric acid as cutting agent.

Preparation

Citric acid can be prepared by reacting a citrate salt with a stronger acid.

Industrially it is extracted from Aspergillus niger cultures. However, because it's dirt cheap, citric acid is easier to buy than to make it yourself.

Projects

Handling

Safety

Being a weak acid, it is not very toxic, but in high concentrations can irritate the skin and sensitive tissues. Ingesting large quantities of citric acid will upset the stomach and cause digestive problems, as well as metabolic acidosis[1].

Storage

Solid citric acid should be stored in closed bottles, in a dry place.

Storage of citrate-containing solutions often promotes the growth of bacteria that may metabolize it. Adding an antibacterial can prevents this.

Disposal

Citric acid can be neutralized before disposal, though this is not always necessary. It can be poured down the drain or dumped in the ground.

References

  1. http://www.annemergmed.com/article/S0196-0644%2801%2984532-7/abstract

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