Disodium octaborate is a
borate
A borate is any of several boron oxyanions, negative ions consisting of boron and oxygen, such as orthoborate , metaborate , or tetraborate ; or any salt with such anions, such as sodium metaborate, and disodium tetraborate . The name also refe ...
of
sodium
Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable iso ...
, 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 with the 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 th ...
, and
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
— a
salt
Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantitie ...
with
elemental formula 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 underst ...
, a white odorless powder. It is used as an
insecticide
Insecticides are substances used to kill insects. They include ovicides and larvicides used against insect eggs and larvae, respectively. Insecticides are used in agriculture, medicine, industry and by consumers. Insecticides are claimed to b ...
,
[ and as a ]fungicide
Fungicides are biocidal chemical compounds or biological organisms used to kill parasitic fungi or their spores. A fungistatic inhibits their growth. Fungi can cause serious damage in agriculture, resulting in critical losses of yield, quality, ...
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 m ...
.[, and as a boron ]micronutrient
Micronutrients are nutrient, essential dietary elements required by organisms in varying quantities throughout life to orchestrate a range of physiological functions to maintain health. Micronutrient requirements differ between organisms; for exam ...
additive in fertilizer
A fertilizer (American English) or fertiliser (British English; see spelling differences) 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 ...
s.[ Trade names include Bora-Care, Borathor, Termite Prufe, Board Defense, Polybor,][ Tim-bor,][ 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 Na2 O. 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 glass ...
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
In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in the orthorhombic sys ...
, with the P21/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 P21/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 small insects that live in colonies and have distinct castes (eusocial) and feed on wood or other dead plant matter. Termites comprise the infraorder Isoptera, or alternatively the epifamily Termitoidae, within the order Blattode ...
s, powder post beetle
Powderpost beetles are a group of seventy species of woodboring beetles classified in the insect subfamily Lyctinae. These beetles, along with spider beetles, death watch beetles, common furniture beetles, skin beetles, and others, make up the ...
s, carpenter ant
Carpenter ants (''Camponotus'' spp.) are large () ants indigenous to many forested parts of the world.
They build nests inside wood consisting of galleries chewed out with their mandibles or jaws, preferably in dead, damp wood. However, unlik ...
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 curren ...
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 is the edible berry of the plant ''Solanum lycopersicum'', commonly known as the tomato plant. The species originated in western South America, Mexico, and Central America. The Mexican Nahuatl word gave rise to the Spanish word ...
and pistachio
The pistachio (, ''Pistacia vera''), a member of the cashew family, is a small tree originating from Central Asia and the Middle East. The tree produces seeds that are widely consumed as food.
''Pistacia vera'' is often confused with other sp ...
, with no observed detrimental effects to the plants.[
]
Safety
Disodium octaborate is not flammable, 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 offspring development. Reproductive toxicants may adversely affect sexual function ...
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 which manages the technical and administrative aspects of the implementation of the European Union regulation called Registration, Evaluation, Authorisation and Restricti ...
(ECHA) to list disodium borate as a Substance of Very High Concern (SVHC) under the (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).]