Disodium octaborate is a

borate A borate is any of a range of boron oxyanions, anions containing boron and oxygen, such as orthoborate , metaborate , or tetraborate ; or any salt of such anions, such as sodium metaborate, and borax . The name also refers to esters of su ...

sodium Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...

, a

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

of sodium,

boron Boron is a chemical element; it has symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the boron group it has three ...

, and

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

— a

salt In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...

with

elemental formula Amino acid-based formula is a type of infant milk formula made from individual amino acids. It is hypoallergenic and intended for infants suffering from severe allergy to milk and various gastrointestinal conditions, such as food protein-induce ...

or , also written as . It is a colorless crystalline solid, soluble in water. Disodium octaborate is traded either as a liquid concentrate, or as the

tetrahydrate In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...

, a white odorless powder. It is used as an

insecticide Insecticides are pesticides used to kill insects. They include ovicides and larvicides used against insect eggs and larvae, respectively. The major use of insecticides is in agriculture, but they are also used in home and garden settings, i ...

, and as a

fungicide Fungicides are pesticides used to kill parasitic fungi or their spores. Fungi can cause serious damage in agriculture, resulting in losses of yield and quality. Fungicides are used both in agriculture and to fight fungal infections in animals, ...

and

algicide Algaecide or algicide is a biocide used for killing and preventing the growth of algae, often defined in a loose sense that, beyond the biological definition, also includes cyanobacteria ("blue-green algae"). An algaecide may be used for controlled ...

, and as a

fire retardant A fire retardant is a substance that is used to slow down or stop the spread of fire or reduce its intensity. This is commonly accomplished by chemical reactions that reduce the flammability of fuels or delay their combustion. Fire retardants ...

., and as a boron

micronutrient Micronutrients are essential chemicals required by organisms in small quantities to perform various biogeochemical processes and regulate physiological functions of cells and organs. By enabling these processes, micronutrients support the heal ...

additive in

fertilizer A fertilizer or fertiliser is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from liming materials or other non-nutrient soil amendments. Man ...

s. Trade names include Bora-Care, Borathor, Termite Prufe, Board Defense, Polybor, Tim-bor, Mr Dotty 008, and Can-Bor.

Preparation

The anhydrous form can be crystallized from a molten mixture of

sodium oxide Sodium oxide is a chemical compound with the formula . It is used in ceramics and glasses. It is a white solid but the compound is rarely encountered. Instead "sodium oxide" is used to describe components of various materials such as glasses and f ...

and

boric oxide Boron trioxide or diboron trioxide is the oxide of boron with the formula . It is a colorless transparent solid, almost always glassy (amorphous), which can be crystallized only with great difficulty. It is also called boric oxide or boria. It h ...

Properties

Solubility

The salt dissolves in water to form forms viscous supersaturated solutions at elevated temperatures. Solubility of the tetrahydrate is 21.9% (wt) at .

Structure

The

anhydrous A substance is anhydrous if it contains no water. Many processes in chemistry can be impeded by the presence of water; therefore, it is important that water-free reagents and techniques are used. In practice, however, it is very difficult to achie ...

salt exists in two stable crystalline forms, α and β. The α form has monoclinic crystal structure, with the P2_1/a space group. The unit cell parameters at 273 K are: ''a'' = 650.7 pm, ''b'' = 1779 pm, ''c'' = 837.7 pm, β = 96.6 °, ''Z'' = 4. The structure contains two interlocking boron-oxygen frameworks, each of them consisting of alternating single and double rings composed of two triangles and a tetrahedron, the so called triborate and pentaborate groups. The two frameworks are connected by two (non-equivalent) sodium atoms, each surrounded by 8 oxygens, comprising finite chains of four polyhedra with shared edges. The thermal expansion is sharply anisotropic, including negative thermal expansion. The thermal expansion tensor in 273–1000 K in function of absolute temperature ''T'' has α₁₁ = 55–0.042''T'', α₂₂ = 11, α₃₃ = -15 + 0.032''T'' (×10–6) K⁻¹, μ = (c^α₃₃) = 42°. The β form has monoclinic crystal structure, with the P2_1/c space group. The unit cell parameters are ''a'' = 1173.1 pm, ''b'' = 788.0 pm, ''c'' = 1041.0 pm, β = 99.883 °, ''Z'' = 4. The structure consists of two infinite, independent, and interleaved boron–oxygen networks containing a complex borate anion formed by six triangles (Δ) and two tetrahedra (T), which can be viewed as a group linked to a group. This fundamental building block is identical to that of the α form and of silver octaborate , with some subtle differences.

Uses

Dilute solutions of disodium octaborate are sprayed on wood surfaces to kill

termite Termites are a group of detritivore, detritophagous Eusociality, eusocial cockroaches which consume a variety of Detritus, decaying plant material, generally in the form of wood, Plant litter, leaf litter, and Humus, soil humus. They are dist ...

s, powder post beetles,

carpenter ant Carpenter ants (''Camponotus'' spp.) are a genus of large ants (workers ) indigenous to many parts of the world. True carpenter ants build nests inside wood, consisting of galleries chewed out with their mandibles or jaws, preferably in dead, ...

s, fungi and algae. The tetrahydrate is also available as pellets for embedding in structural wood. Compared to other chemicals used for these purposes, it has the advantages of lack of odor, permanent effect, and low toxicity to humans and pets. The compound was also shown to significantly reduce

dust mite House dust mites (HDM, or simply dust mites) are various species of acariform mites belonging to the family Pyroglyphidae that are found in association with dust in dwellings. They are known for causing allergies. Biology Species The current ...

populations in the home when applied as a dilute solution to carpets and upholstery together with regular vacuum cleaning. Disodium octaborate, applied to the soil or foliar spray, has been shown to inhibit pests of crops such as

tomato The tomato (, ), ''Solanum lycopersicum'', is a plant whose fruit is an edible Berry (botany), berry that is eaten as a vegetable. The tomato is a member of the nightshade family that includes tobacco, potato, and chili peppers. It originate ...

and

pistachio The pistachio (, ; ''Pistacia vera'') is a small to medium-sized tree of the Anacardiaceae, cashew family, originating in Iran. The tree produces nut (fruit)#Culinary definition and uses, seeds that are widely consumed as food. In 2022, world ...

, with no observed detrimental effects to the plants.

Safety

Disodium octaborate is neither flammable, nor combustible or explosive and has low acute oral and dermal toxicity. The oral 50% lethal doses (LD50) are 5.3 g/kg for guinea pig, 2g/kg for rats. However, it is classified as "

reproductive toxicity Reproductive toxicity refers to the potential risk from a given chemical, physical or biologic agent to adversely affect both male and female fertility as well as teratogen, offspring development. Reproductive toxicants may adversely affect sexu ...

category 1B (presumed human reproductive toxicant)" under the EU Classification, Labelling and Packaging Regulation (

CLP Regulation The CLP Regulation (for "Classification, Labelling and Packaging") is a European Union regulation from 2008, which aligns the European Union system of classification, labelling and packaging of chemical substances and mixtures to the Globally ...

). The CLP hazard code and statement are "H360FD: May damage fertility. May damage the unborn child." On 22 February 2018, the Swedish Chemicals Agency (KEMI) submitted a proposal to the

European Chemicals Agency The European Chemicals Agency (ECHA; ) is an agency of the European Union working for the safe use of chemicals. It manages the technical and administrative aspects of the implementation of the European Union regulation called Registration, E ...

(ECHA) to list disodium borate as a Substance of Very High Concern (SVHC) under the

Registration, Evaluation, Authorisation and Restriction of Chemicals Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) is a European Union regulation dating from 18 December 2006, amended on 16 December 2008 by Regulation (EC) No 1272/2008. REACH addresses the production and use of che ...

(REACH) Regulation.

References

Proposal for Identification of a Substance of Very High Concern on the Basis of the Criteria Set Out in REACH Article 57
, Swedish Chemicals Agency, 22 February 2018. Polybor
. Product data page at the U. S. Borax company website. Accessed on 2022-06-27.
. Product data page at the U. S. Borax company website. Accessed on 2022-06-27. B.J Brotherton Boron: Inorganic Chemistry Encyclopedia of Inorganic Chemistry (1994) Ed. R. Bruce King, John Wiley & Sons Disodium octaborate
. Substance page at the National Institutes of Health - National Library of Medicine ''ChemDplus'' website. Accessed on 2022-06-28. Boron sodium oxide (B8Na2O13)
. Substance page at the ''PubChem'' website. Accessed on 2022-06-28. M. Briggs (2001): "Boron Oxides, Boric Acid, and Borates". Chapter of the ''Kirk-Othmer Encyclopedia of Chemical Technology''. Wiley. H. W. Scherer et al (2008): "Fertilizers". Chapter of ''Ullmann's Encyclopedia of Industrial Chemistry'', 7th ed. C. J. Leedecke and C. G. Bergeron (1977): "Crystallisation of Na₂B₈O₁₃ in Selected Na₂O-B₂O₃ Melts". ''Physics and Chemistry of Glasses'' (UK), volume 18, issue 6, pages 116-120. H. Kavak, A. L. Tuna, and H. S. Civelek (2017): "Effects of Tarımbor (Na₂B₈O₁₃.4(H₂O)) fertiliser against Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) and biochemistry and physiology of tomato plants under greenhouse conditions." ''Ege Üniversitesi Ziraat Fakültesi Dergisi'', volume 54, issue 2, pages 157-165 (in Turkish). {{Borates Borates Sodium compounds