ADDkid: NaOBr is temperature sensitive. Lets take a closer look at the procedure marked in red.
2 NaOH + Br2 ==> NaOBr + NaBr
A solution of 42 g. (1.05 moles) of sodium hydroxide in 360 ml. of water is placed in a 1-l. three-necked, round-bottomed flask fitted with a mechanical stirrer and
a thermometer and is cooled to -5° in an ice-salt bath. The stirrer is started, and 43 g. (0.263 mole) of bromine
is added from a separatory funnel at such a rate that the temperature remains below 0° (addition time about 5 minutes). The ice-cold solution is diluted with 240 ml. of dioxane (Note 1) that has previously been cooled to 13–14° (Note 2).
This solution is kept at 0° until required.2.
The temperature of the hypobromite solution is kept below 10° to avoid the formation of sodium bromate.
I mention that adding hydrogen peroxide to HBr until neutral, and then adding the NaOH
If you intend to make the Br first (hydrogen peroxide to HBr until neutral) and add the NaOH, YOU MUST CONTROL THE TEMPERATURE DURING THE REACTION.