1,5-Naphthalene diisocyanate

Description

Naphthalene diisocyanate (NDI) occurs as white to lightyellow crystalline flakes with a characteristic odor. NDI is incompatible with many classes of compounds, reacting exothermically to release toxic gases. Reactions with amines, aldehydes, alcohols, alkali metals, ketones, mercaptans, strong oxidizers, hydrides, phenols, and peroxides can cause vigorous releases of heat. Acids and bases initiate polymerization reactions. NDI can react with water to form amines and liberate carbon dioxide.

Chemical Properties

Naphthylene 1,5-diisocyanate is a solid, m.p. 128°C. It has a lower vapour pressure than tolylene diisocyanate and is therefore less toxic in use; it does, however, have sensitizing properties.

Uses

Naphthylene 1,5-diisocyanate is mainly used for the production of elastomers.

Uses

NDI is used as a curing agent in the manufacture of elastomers.

Uses

Manufacture of polyurethane solid elastomers.

Definition

ChEBI: 1,5-Naphthalene diisocyanate is a member of naphthalenes.

Preparation

Naphthylene 1,5-diisocyanate (NDI) is prepared from naphthalene as follows:

General Description

White to light-yellow crystalline flakes.

Reactivity Profile

Isocyanates and thioisocyanates, such as 1,5-Naphthalene diisocyanate, are incompatible with many classes of compounds, reacting exothermically to release toxic gases. Reactions with amines, aldehydes, alcohols, alkali metals, ketones, mercaptans, strong oxidizers, hydrides, phenols, and peroxides can cause vigorous releases of heat. Acids and bases initiate polymerization reactions in these materials. Some isocyanates react with water to form amines and liberate carbon dioxide. Base-catalysed reactions of isocyanates with alcohols should be carried out in inert solvents. Such reactions in the absence of solvents often occur with explosive violence, [Wischmeyer(1969)].

Hazard

Irritant. Questionable carcinogen.

Flammability and Explosibility

Non flammable

Safety Profile

A powerful allergen. An irritant. Questionable carcinogen. When heated to decomposition it emits toxic fumes of NOx.

Environmental Fate

NDI is a synthetic organic chemical. It is a natural derivative of primary amines with the general formula R–N]C]O which does not occur naturally in the environment. At room temperature it can be a liquid or crystal. It is miscible with alcohol, diglycol, monoethyl ether, ether, acetone, carbon tetrachloride, benzene, chlorobenzene, kerosene, and olive oil; however, it may react violently with alcohol, water, acid, bases, and strong alkaline materials and tertiary amines and generate enough heat to self-ignite and release toxic combustion products. NDI is not readily biodegradable; however, it reacts with water and most acids producing unstable carbonic acids, which subsequently decarboxylate yielding relatively chemically inert and insoluble polymeric urea. While these polyureas are persistent, studies have indicated that they pose virtually no potential for adverse impacts on the aquatic environment. Due to hydrolysis in water, bioaccumulation of NDI is not expected. Since the hydrolysis products formed are irritants, there is a potential for inhalation exposure. The degree stability is a function of humidity.

Toxicity evaluation

The toxicological properties of isocyanates are attributed to the –N=C=O group. It is thought to react vigorously and exothermically with water forming an unstable carbamic acid that dissociates to form a primary amine with liberation of CO2. Hence, the primary amine will react further generating a urea derivative. Isocyanates also react readily with all organic compounds resulting in polymerization. Such reactions denature proteins, form abnormal crosslinkages, and generally disorganize the protein resulting in alteration of its normal function. This reactivity with proteins can account for its potency as a sensitizing agent. An IgE- or IgG-mediated mechanism has been proposed, but has not been definitively linked to isocyanate exposure. There is also evidence that inflammation and morphological changes of the bronchia mucosa and direct neurogenic mechanisms could be involved in the mechanics of toxicity. Thus, more than one reaction may occur in a system at a given time.