What's the melting point of aspirin?

Question

some books says 135
other says 138-140

whats the correct

Answer 1

The problem with getting a value for the melting point of an organic substance is the purity of the material. A pure sample of a substance will melt at a sharply defined temperature, an impure sample will show a larger range. It also helps to know the source of the information -- some sources are more rigorously researched than others.

Here are some values from some standard references I have; see what you think is the more correct answer:

Aspirin (acetylsalicylic acid, 2-(acetyloxy)-benzoic acid, 2-Acetylbenzoic acid), CAS # 50-78-2, MW = 180.16

CRC Handbook of Chemistry and Physics, 83d Ed.: MP = 135°C
Merck Index, 13th Ed.: MP = 135°C
Systematic Identification of Organic Componds, 7th Ed.: MP = 135°C
Hazardous Chemicals Desk Reference, 2d Ed.: MP = 135°C
Handbook of Organic Chemistry, J.A. Dean: MP = 135°C
Lange's Handbook of Chemistry, 13th Ed.: MP = 135°C
MSDS for Aspirin from the University of Iowa: MP = 135°C
MSDS for Aspirin from J.T. Baker Chemicals: MP = 135°C

Wikipedia: MP = 138 - 140 °C
Aldrich Chemicals Catalog for 99+%: MP = 138 - 140°C
MSDS for Aspirin from Oxford University: MP = 138 - 140°C
MSDS for 99% Aspirin from Fisher Chemicals: MP = 138 - 140°C

Answer 2

This Site Might Help You.

RE:
What's the melting point of aspirin?
some books says 135
other says 138-140

whats the correct

Answer 3

Msds For Aspirin

Answer 4

(m)

How to Make Aspirin - Acetylsalicylic Acid - Procedure
Accurately weigh 3.00 grams of salicylic acid and transfer to a dry Erlenmeyer flask. If you will be calculating actual and theoretical yield, be sure to record how much salicylic acid you actually measured.
Add 6 mL of acetic anhydride and 5-8 drops of 85% phosphoric acid to the flask.
Gently swirl the flask to mix the solution. Place the flask in a beaker of warm water for ~15 minutes.
Add 20 drops of cold water dropwise to the warm solution to destroy the excess acetic anhydride.
Add 20 mL of water to the flask. Set the flask in an ice bath to cool the mixture and speed crystallization.
When the crystallization process appears complete, pour the mixture through a Buckner funnel.
Apply suction filtration through the funnel and wash the crystals with a few milliliters of ice cold water. Be sure the water is near freezing to minimize loss of product.
Perform a recrystallization to purify the product. Transfer the crystals to a beaker. Add 10 mL of ethanol. Stir and warm the beaker to dissolve the crystals.
After the crystals have dissolved, add 25 mL of warm water to the alcohol solution. Cover the beaker. Crystals will reform as the solution cools. Once crystallization has started, set the beaker in an ice bath to complete the recrystallization.
Pour the contents of the beaker into a Buckner funnel and apply suction filtration.
Remove the crystals to dry paper to remove excess water.
Confirm you have acetylsalicylic acid by verifying a melting point of 135°C.