why would it be undesirable to wash the crude halide with aqueous sodium hydroxide
Without knowing what you're doing and which sodium halide you are talking about, my best guess is that the halide is soluble in water AND it may be likely to form the OX^- ion.
Washing the crude halide with aqueous sodium hydroxide (NaOH) can be undesirable for several reasons.
1. Formation of unwanted products: The reaction between the crude halide and aqueous sodium hydroxide can lead to the formation of undesired products. Halides, such as chlorides, bromides, or iodides, can react with NaOH to form halogen gas (Cl2, Br2, or I2) and sodium halide salts. These byproducts may contaminate the desired product and make it impure.
2. Loss of desired product: Washing the crude halide with sodium hydroxide can result in the loss of the desired product through solubility. Some organic compounds may dissolve or react with NaOH, leading to the loss of the desired compound from the crude mixture.
3. Altered chemical reactivity: Sodium hydroxide is a strong base and can modify the chemical properties of organic compounds. It can cause hydrolysis or cleavage of functional groups, resulting in the degradation or transformation of the desired compound. This may lead to a decrease in the yield or quality of the final product.
If you want to avoid washing the crude halide with aqueous sodium hydroxide, alternative methods can be employed. For example, you can consider using a different solvent or purifying agent that does not react with or dissolve the desired compound. It is crucial to determine a purification method that is compatible with the specific properties of the crude halide and the desired product.