The basic idea

In common syntheses of aspirin, salicylic acid is treated with acetic anhydride, causing a chemical reaction that turns salicylic acid's hydroxyl group into an ester group. Because acetic anhydride is used for the synthesis of heroin by the diacetylation of morphine, acetic anhydride is listed as a U.S. DEA List II precursor, and therefore it is restricted in many other countries including mine, so I won't use it. Instead I'll follow a slightly different path as a starting point:

As acetic acid is less reactive than acetic anhydride, the reaction yield will be lower. Furthermore the purity level of the acetyl-salicylic acid will be lower.

Balanced equation:

\color{White} \large C_7H_6O_3+C_2H_4O_2 \rightarrow C_9H_8O_4+H_2OMolar mass salicylic acid: 138.122 g/mol

Molar mass acetic acid: 60.052 g/mol

Molar mass acetyl-salicylic acid: 180.157 g/mol

Molar mass water: 18.015 g/mol

Theoretical yield:

138.122 g salicylic acid + 60.052 g acetic acid → 180.157 g acetyl-salicylic acid

But I expect the actual yield will be only half of the theoretical one.

Synthesis of aspirin at a laboratory scale






Testing for Impurities

Iron(III) chloride can be used to determine the purity of the synthesized aspirin. Iron(III) chloride forms a purple complex with the phenol group. Salicylic acid is a phenol. It cannot be removed by using cold distilled water as its solubility in water is poor. So if salicylic acid is still present, the product will turn purple when Iron(III) chloride is added.

Synthesis of salicylic acid at a laboratory scale

Salicylic acid can be synthesized by a base-catalyzed hydrolysis of methyl salicylate, commonly known as oil of wintergreen or wintergreen oil:

Balanced equation:

\color{White} \large C_8H_8O_3+2~NaOH+H_2SO_4  \rightarrow C_7H_6O_3 + Na_2SO_4 + CH_3OH + H_2O As we can see, side products are water, sodium sulfate and methanol. The hydrate of sodium sulfate is known as Glauber's Salt, a formerly used general purpose laxative. Methanol is the simplest alcohol and highly toxic.

Molar mass methyl salicylate: 152.15 g/mol

Molar mass sodium hydroxide: 39.9971 g/mol

Molar mass sulfuric acid: 98.079 g/mol

Molar mass sodium sulfate: 142.04 g/mol

Molar mass methanol: 32.04 g/mol

Therefore theoretically:

152.15 g methyl salicylate + 79.9942 g sodium hydroxide + 98.079 g sulfuric acid → 138.122 g salicylic acid + 142.04 g sodium sulfate + 32.04 g methanol + 18.015 g water

Lab synthesis procedure:




Aspirin lab-on-a-chip

A lab-on-a-chip (LOC) is a device that integrates one or several laboratory functions on a single chip of only millimeters to a few square centimeters in size.

The rendering below shows a jacketed condenser apparatus, put together in sandwich construction, milled out from two borosilicate glass plates. The heating element is just a 1.5 Ω 50W electrical resistor as it is used in hot beds of 3-D printer.

Another possibility would be to 3-D print structure of apparatus with fire-proof and chemical resistant silicone on carrier glass plates:

The chemputer

A chemputer is a kind of 3-D printer that 'uses a bathroom sealant as a material to print reaction chambers of precisely specified dimensions, connected with tubes of different lengths and diameters. After the bespoke miniature lab had set hard, the printer could then inject the system reactants, or "chemical inks", to create sequenced reactions'.

Well, it is basically a LoC 3-D printer, injecting automatically chemicals into it. But why not 3-D print chemical reactants itself on a near molecular level to react with eatch other on a carrier?