1,3-Dimethylurea
[CAS 96-31-1]

Identification

• Classification: Organic raw materials >> Alkyl ureas and their derivatives and salts
• Name: 1,3-Dimethylurea
• Synonyms: N,N'-Dimethylurea
• Molecular Formula: C₃H₈N₂O
• Molecular Weight: 88.11
• CAS Registry Number: 96-31-1
• EC Number: 202-498-7
• SMILES: CNC(=O)NC

Properties

• Density: 0.9±0.1 g/cm³ Calc.^*, 1.14 g/mL (Expl.)
• Melting point: 101 - 104 °C (Expl.)
• Boiling point: 269.0 °C 760 mmHg (Calc.)^*, 268 - 270 °C (Expl.)
• Flash point: 124.3±18.9 °C (Calc.)^*, 157 °C (Expl.)
• Solubility: water: 765 g/L (21.5 °C) (Expl.)
• Index of refraction: 1.414 (Calc.)^*

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Safety Data

• Hazard Symbols: GHS08 Warning
• Risk Statements: H373
• Safety Statements: P501-P260-P314

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Specific target organ toxicity - repeated exposure	STOT RE	2	H373
Reproductive toxicity	Repr.	2	H361

chemBlink Chemical Story

1,3-Dimethylurea, CAS 96-31-1, is a symmetrical substituted urea used as an intermediate and reagent in organic synthesis. It is also known as N,N'-dimethylurea or sym-dimethylurea. Its molecular formula is C₃H₈N₂O and its molecular weight is 88.11. Its structure can be written as CH₃NHCONHCH₃.

The molecule is derived from urea, NH₂CONH₂, by replacing one hydrogen on each nitrogen with a methyl group.

That apparently simple change gives 1,3-dimethylurea an important synthetic identity.

The two methyl groups are arranged symmetrically, one on each nitrogen. When the urea unit is transformed into a nitrogen-containing ring, those methyl groups can travel with the nitrogen atoms and become part of the substitution pattern of the final heterocycle.

This principle appears in the classical chemistry of caffeine and theophylline.

Caffeine and theophylline belong to the methylxanthine family. Their fused nitrogen-containing ring systems look far more complicated than 1,3-dimethylurea, yet part of their substitution pattern can be traced back to a remarkably simple dimethylated urea precursor.

Official OECD chemical-assessment documentation specifically records symmetrical N,N'-dimethylurea as an intermediate for the synthesis of caffeine by the Traube method and as an intermediate for pharmaceuticals including theophylline and caffeine.

The Traube purine synthesis is one of the classical routes for constructing purine-related heterocycles. In this chemistry, substituted ureas can be combined with carbon-containing reagents to build pyrimidine intermediates that are subsequently elaborated into fused purine systems.

An important intermediate obtainable from 1,3-dimethylurea is 1,3-dimethyl-6-aminouracil.

A published reagent review notes that this compound was prepared from 1,3-dimethylurea, cyanoacetic acid, and acetic anhydride. The transformation converts a simple open-chain urea derivative into a six-membered nitrogen-containing heterocycle.

That is already a major increase in molecular complexity.

The two methyl groups, however, have not been randomly added during ring construction. They were present from the beginning on the two nitrogens of 1,3-dimethylurea.

This is one reason substituted ureas are useful synthetic starting materials. They allow chemists to decide part of the nitrogen-substitution pattern before the heterocyclic ring has even been built.

The relationship can be viewed as a form of molecular preprogramming.

The small starting material already contains information about which nitrogen atoms will carry methyl groups later.

Additional carbon-carbon and carbon-nitrogen bonds are then constructed around that prearranged nitrogen-carbonyl framework.

1,3-Dimethylurea is not limited to methylxanthine chemistry. It is a versatile reagent for constructing other nitrogen-containing heterocycles, including pyrimidine derivatives.

For example, it can participate in Biginelli-type multicomponent reactions.

The classical Biginelli reaction combines a urea-type compound, an aldehyde, and a carbonyl compound to produce a dihydropyrimidine ring. Substituting 1,3-dimethylurea for ordinary urea changes the nitrogen substitution already present in the resulting heterocyclic framework.

Again, the methyl groups act as structural information carried from a simple reagent into a more complicated ring system.

The compound has another, very different use in industrial reaction research.

Urea-formaldehyde chemistry is enormously important in adhesives and resins, especially materials associated with wood products. Unfortunately, the actual urea-formaldehyde reaction network is complicated because urea contains several reactive N-H positions and can ultimately form polymeric structures.

Researchers have therefore used 1,3-dimethylurea as a simpler model.

A detailed quantitative nuclear magnetic resonance study investigated the reaction of 1,3-dimethylurea with formaldehyde specifically as a model for the industrially important urea-formaldehyde system.

The methyl groups simplify the chemistry by blocking two of the reactive positions present in urea.

The researchers found a much smaller reaction network involving hydroxymethylation, hemiformal formation, and condensation leading to methylene and ether bridges.

Unlike ordinary urea-formaldehyde chemistry, however, the 1,3-dimethylurea-formaldehyde model system does not continue into polymer formation.

This makes the compound useful not because it perfectly reproduces the industrial material, but because it removes some of the complexity.

Chemists often learn about a complicated reaction network by deliberately studying a simpler molecule in which some reaction pathways have been blocked.

1,3-Dimethylurea therefore acts almost like a controlled laboratory version of urea.

Two methyl groups say, in effect:

these two nitrogen positions are already occupied.

Study what the remaining positions can do.

More recently, 1,3-dimethylurea appeared in a completely different area of synthetic chemistry: electrochemical reduction.

The Birch reduction is a famous reaction in which aromatic rings are converted into partially reduced cyclic structures. The traditional procedure is strongly associated with alkali metals such as sodium or lithium dissolved in liquid ammonia.

Although extremely useful, those conditions create practical challenges, particularly when reactions must be performed safely and on larger scale.

In 2019, researchers reported in Science a scalable electrochemical alternative inspired by lithium-ion battery chemistry.

Instead of relying on the classical combination of alkali metal and liquid ammonia, the reaction used an electrochemical cell.

1,3-Dimethylurea was included as a proton donor in the reaction system.

This is a strikingly different role from its use in caffeine chemistry.

In one case, its atoms become part of a growing heterocyclic molecule.

In the other, it helps provide hydrogen during an electrochemical transformation and is not intended to become the carbon skeleton of the product.

The same simple molecule can therefore perform very different jobs depending on the reaction environment.

Its history also spans very different periods of chemistry.

Substituted ureas belong to classical heterocyclic chemistry developed more than a century ago.

Yet 1,3-dimethylurea also appears in modern electrochemical synthesis designed around safer and more scalable alternatives to historically demanding reactions.

The molecule itself has not changed.

What chemists ask it to do has.

That makes 1,3-dimethylurea a useful reminder that the value of a chemical reagent is not determined by how complicated its structure looks.

Three carbon atoms are enough.

In one reaction, they help prearrange the nitrogen substitution of a future heterocycle.

In another, methyl substitution deliberately simplifies a complicated formaldehyde reaction network.

In still another, the molecule becomes part of a modern electrochemical reduction system.

Sometimes a very small structural modification of urea is enough to turn one familiar molecule into several different chemical tools.

References

1. NIST Chemistry WebBook. Urea, N,N'-dimethyl-, CAS 96-31-1. Molecular formula C₃H₈N₂O; molecular weight 88.1084.

2. OECD SIDS. 1,3-Dimethylurea, CAS 96-31-1. Uses including synthesis of caffeine by the Traube method and intermediacy in pharmaceutical synthesis.

3. Das, S. (2010). "N,N'-Dimethyl Urea." Synlett, 2010, 1138-1139.

4. Steinhof, O.; Scherr, G.; Hasse, H. (2016). "Investigation of the reaction of 1,3-dimethylurea with formaldehyde by quantitative on-line NMR spectroscopy: a model for the urea-formaldehyde system." Magnetic Resonance in Chemistry, 54, 457-476.

5. Peters, B. K. et al. (2019). "Scalable and safe synthetic organic electroreduction inspired by Li-ion battery chemistry." Science, 363, 838-845.

6. Published studies concerning Biginelli reactions and the synthesis of dihydropyrimidines using 1,3-dimethylurea.